Lobular Versus Ductal Breast Neoplasms

Florid Lobular Carcinoma In Situ: Imaging Characteristics and Pathologic Upgrade Rates on Surgical Excision

Background: Florid lobular carcinoma in situ is an uncommon lobular neoplasia variant that is frequently associated with invasive carcinoma. However, there remains a paucity of information to guide management. The authors aimed to study imaging features associated with pathologic upgrade rates for patients with florid lobular carcinoma in situ identified on core biopsy undergoing surgical excision. Methods: Patients with florid lobular carcinoma in situ on core biopsy were selected from an institutional pathology database. Patients were excluded if pleomorphic lobular carcinoma in situ was also present on core biopsy. Clinical, radiologic, and pathologic features for each case were reviewed focusing on imaging features which led to core biopsy and those associated with pathologic upgrade on surgical excision. Results: Eighteen cases of florid lobular carcinoma in situ underwent surgical excision. Upgrade rates on surgical excision were higher in cases with suspicious calcifications (8/11, 73%, p=0.049) compared to those without (1/7, 14.3%) and in cases with larger breast lesions (p=0.011). The overall upgrade rate was 50% (9/18), 89% (8/9) with invasive lobular carcinoma and 11% (1/9) with ductal carcinoma in situ. Of the 8 cases with upgrade to invasive lobular carcinoma, 7/8 (87.5%) were Stage I cancers and only 1/8 (12.5%) had macroscopic lymph node involvement and was upgraded to Stage II. Conclusion: Florid lobular carcinoma in situ on core biopsy had an upgrade rate on surgical excision of 50% overall, with 89% of these cases upgraded to invasive lobular carcinoma. Pathologic upgrade was seen more frequently with suspicious calcifications and larger breast lesions. These findings can help guide surgical management of this uncommon lobular neoplasia variant including planning extent of excision and consideration for lymph node evaluation.

Unique Molecular Alteration of Lobular Breast Cancer: Association with Pathological Classification, Tumor Biology and Behavior, and Clinical Management

Invasive lobular carcinoma (ILC), accounting for up to 15% of diagnosed breast cancers, has garnered significant attention due to the loss of the epithelial cell-cell adhesion molecule E-cadherin. This loss contributes to its distinct biological, morphological, and clinical characteristics compared to non-lobular breast cancers. The use of immunohistochemistry (IHC) for E-cadherin and/or the associated cadherin-catenin complex, such as p120-catenin and beta-catenin, in morphologically equivocal cases, has been increasingly adopted in pathology practice. This approach has substantially improved diagnostic accuracy, interobserver reproducibility, and the identification of new morphologic variants of ILC. ILCs exhibit unique tumor biology, which presents considerable challenges in clinical management, especially in preoperative imaging evaluation, surgical management, and neoadjuvant treatment. Recent advances in translational and clinical research have enhanced our understanding of ILC and have spurred the development of new clinical trials specifically targeting these cancers. This review highlights recent progress in various aspects of ILC, including its unique molecular alteration, pathological classification and diagnostic approach, tumor biology and behavior, key clinical management challenges, and ongoing clinical trials, as well as the role of artificial intelligence in diagnosing ILC radiologically and pathologically. The goal of this review is to provide an updated understanding of the tumor biology, clinical manifestations, and molecular landscape of ILC and to help refine current tumor classification and diagnosis, subsequently improving management strategies and overall outcomes for lobular carcinoma patients.

Comprehensive characterization of invasive mammary carcinoma with lobular features: integrating morphology and E-cadherin immunohistochemistry patterns

BACKGROUND

Breast cancer treatment prioritizes molecular subtypes over histologic types. However, considering the unique biological behavior of invasive lobular carcinoma (ILC), its diagnosis is crucial for patient management. Therefore, this study aimed to review breast cancer cases, focusing on the E-cadherin patterns and lobular morphology of cases misclassified in the original reports.

METHODS

A comprehensive review was conducted on 481 breast cancer biopsy cases diagnosed as invasive breast carcinoma of no special type (IBC-NST) or ILC with E-cadherin staining. These cases were categorized into six groups based on tumor morphology (ductal/lobular) and E-cadherin expression pattern (membranous/loss/aberrant): (1) ductal/membranous, (2) lobular/loss, (3) lobular/aberrant, (4) mixed, (5) ductal/loss or aberrant, and (6) lobular/membranous.

RESULTS

In 211 cases (43.8%), an E-cadherin pattern indicating ILC (loss and aberrant) was observed alongside lobular morphology, representing 5.52% of all breast cancer biopsies during the relevant period. Moreover, 181 cases (37.6%) showed a membranous pattern with ductal morphology, 4 (0.8%) were mixed IBC-NST and ILC, and 85 (17.7%) exhibited discordance between morphology and E-cadherin expression. Notably, only 25.9% (15/58) of cases in group 3, characterized by aberrant E-cadherin patterns, were initially diagnosed as ILC, highlighting a significant diagnostic discrepancy. In group 6, where membranous E-cadherin pattern was present with lobular morphology, only 3.4% (2/58) were diagnosed as ILC in the original reports, indicating diagnostic challenges in morphology and immunohistochemistry discordance. Similarly, in group 5, which had ductal morphology with loss or aberrant E-cadherin expression, the initial diagnosis rate of IBC-NST was 33.3% (9/27), reflecting the complexities in interpreting discordant cases.

CONCLUSIONS

In real-world practice, diagnosing ILC often heavily depends on E-cadherin results. This study emphasizes the need for diagnostic clarification in cases with discordance between morphology and E-cadherin patterns.

"Lobular lesions of the breast: From the classic to the variants"

The aim of this review is to provide the surgical pathologist an overview of lobular lesions, from in situ to invasive carcinoma and the variants, by discussing the epidemiology, clinical characteristics, morphology, immunohistochemistry, known molecular data as well as the treatment recommendations. The recognition of histologic variants of both in situ and invasive lobular carcinoma has expanded the differential diagnosis. Awareness of these different entities is important as treatment recommendations continue to evolve.

Functions of p120-catenin in physiology and diseases

p120-catenin (p120) plays a vital role in regulating cell-cell adhesion at adherens junctions, interacting with the juxtamembrane domain (JMD) core region of E-cadherin and regulates the stability of cadherin at the cell surface. Previous studies have shown significant functions of p120 in cell-cell adhesion, tumor progression and inflammation. In this review, we will discuss recent progress of p120 in physiological processes and diseases, and focus on the functions of p120 in the regulation of cancer and inflammation.

Spatial molecular profiling of mixed invasive ductal and lobular breast cancers reveals heterogeneity in intrinsic molecular subtypes, oncogenic signatures, and mutations

Mixed invasive ductal and lobular carcinoma (MDLC) is a rare histologic subtype of breast cancer displaying both E-cadherin positive ductal and E-cadherin negative lobular morphologies within the same tumor, posing challenges with regard to anticipated clinical management. It remains unclear whether these distinct morphologies also have distinct biology and risk of recurrence. Our spatially resolved transcriptomic, genomic, and single-cell profiling revealed clinically significant differences between ductal and lobular tumor regions including distinct intrinsic subtype heterogeneity - e.g., MDLC with triple-negative breast cancer (TNBC) or basal ductal and estrogen receptor positive (ER+) luminal lobular regions, distinct enrichment of cell cycle arrest/senescence and oncogenic (ER and MYC) signatures, genetic and epigenetic CDH1 inactivation in lobular but not ductal regions, and single-cell ductal and lobular subpopulations with unique oncogenic signatures further highlighting intraregional heterogeneity. Altogether, we demonstrated that the intratumoral morphological/histological heterogeneity within MDLC is underpinned by intrinsic subtype and oncogenic heterogeneity which may result in prognostic uncertainty and therapeutic dilemma.

Spatial molecular profiling of mixed invasive ductal-lobular breast cancers reveals heterogeneity in intrinsic molecular subtypes, oncogenic signatures, and mutations

Mixed invasive ductal and lobular carcinoma (MDLC) is a rare histologic subtype of breast cancer displaying both E-cadherin positive ductal and E-cadherin negative lobular morphologies within the same tumor, posing challenges with regard to anticipated clinical management. It remains unclear whether these distinct morphologies also have distinct biology and risk of recurrence. Our spatially-resolved transcriptomic, genomic, and single-cell profiling revealed clinically significant differences between ductal and lobular tumor regions including distinct intrinsic subtype heterogeneity (e.g., MDLC with TNBC/basal ductal and ER+/luminal lobular regions), distinct enrichment of senescence/dormancy and oncogenic (ER and MYC) signatures, genetic and epigenetic CDH1 inactivation in lobular, but not ductal regions, and single-cell ductal and lobular sub-populations with unique oncogenic signatures further highlighting intra-regional heterogeneity. Altogether, we demonstrated that the intra-tumoral morphological/histological heterogeneity within MDLC is underpinned by intrinsic subtype and oncogenic heterogeneity which may result in prognostic uncertainty and therapeutic dilemma.

Significance

MDLC displays both ductal and lobular tumor regions. Our multi-omic profiling approach revealed that these morphologically distinct tumor regions harbor distinct intrinsic subtypes and oncogenic features that may cause prognostic uncertainty and therapeutic dilemma. Thus histopathological/molecular profiling of individual tumor regions may guide clinical decision making and benefit patients with MDLC, particularly in the advanced setting where there is increased reliance on next generation sequencing.

Upgrade Rates of Variant Lobular Carcinoma In Situ Compared to Classic Lobular Carcinoma In Situ Diagnosed in Core Needle Biopsies: A 10-Year Single Institution Retrospective Study

The primary aim of this study was to determine the upgrade rates of variant lobular carcinoma in situ (V-LCIS, ie, combined florid [F-LCIS] and pleomorphic [P-LCIS]) compared with classic LCIS (C-LCIS) when diagnosed on core needle biopsy (CNB). The secondary goal was to determine the rate of progression/development of invasive carcinoma on long-term follow-up after primary excision. After institutional review board approval, our institutional pathology database was searched for patients with "pure" LCIS diagnosed on CNB who underwent subsequent excision. Radiologic findings were reviewed, radiologic-pathologic (rad-path) correlation was performed, and follow-up patient outcome data were obtained. One hundred twenty cases of LCIS were identified on CNB (C-LCIS = 97, F-LCIS = 18, and P-LCIS = 5). Overall upgrade rates after excision for C-LCIS, F-LCIS, and P-LCIS were 14% (14/97), 44% (8/18), and 40% (2/5), respectively. Of the total cases, 79 (66%) were deemed rad-path concordant. Of these, the upgrade rate after excision for C-LCIS, F-LCIS, and P-LCIS was 7.5% (5 of 66), 40% (4 of 10), and 0% (0 of 3), respectively. The overall upgrade rate for V-LCIS was higher than for C-LCIS (P = .004), even for the cases deemed rad-path concordant (P value: .036). Most upgraded cases (23 of 24) showed pT1a disease or lower. With an average follow-up of 83 months, invasive carcinoma in the ipsilateral breast was identified in 8/120 (7%) cases. Six patients had died: 2 of (contralateral) breast cancer and 4 of other causes. Because of a high upgrade rate, V-LCIS diagnosed on CNB should always be excised. The upgrade rate for C-LCIS (even when rad-path concordant) is higher than reported in many other studies. Rad-path concordance read, surgical consultation, and individualized decision making are recommended for C-LCIS cases. The risk of developing invasive carcinoma after LCIS diagnosis is small (7% with ∼7-year follow-up), but active surveillance is required to diagnose early-stage disease.

Case report: Cutaneous metastases as a first manifestation from breast cancer with concurrent gastric metastases

Background: Breast cancer represents a leading cause of malignancy among Chinese women, posing a significant health burden. The diagnosis of metastatic breast cancer, particularly to uncommon sites like the skin and stomach, presents distinct challenges. Case introduction: This case report describes a 71-year-old Chinese women with a persistent back rash lasting more than 6 months. Physical examination revealed red papules on her back. Immunohistochemistry confirmed positive for cytokeratin 7(CK7), GATA-3 and GCDFP15, as well as negative staining of cytokeratin 20 (CK20), suggesting breast cancer metastasis. Further evaluation revealed a breast nodule and axillary lymph node enlargement, with biopsies confirming invasive lobular carcinoma (ILC). Abdominal computed tomography (CT) revealed thickening of the gastric and ascending colon walls. Gastroscopy revealed chronic superficial atrophic gastritis. However, gastric metastasis was further confirmed by pathology. The patient initiated endocrine therapy with fulvestrant and exemestane, resulting in rash resolution and stable breast and stomach lesions after 3 months. Overall, the patient is experiencing an improvement in her condition and remains stable while continuing treatment. Conclusion: This case highlights the importance of considering atypical metastatic patterns in breast cancer and the potential efficacy of endocrine therapies in managing such cases. Moreover, it emphasizes the need for vigilance in breast cancer patients, especially those with ILC, as gastrointestinal symptoms may indicate gastric metastasis (GMs). Ultimately, early detection and appropriate treatment strategies, such as endocrine therapy, can contribute to improved outcomes in these challenging cases.

European guidelines for the diagnosis, treatment and follow-up of breast lesions with uncertain malignant potential (B3 lesions) developed jointly by EUSOMA, EUSOBI, ESP (BWG) and ESSO

INTRODUCTION

Breast lesions of uncertain malignant potential (B3) include atypical ductal and lobular hyperplasias, lobular carcinoma in situ, flat epithelial atypia, papillary lesions, radial scars and fibroepithelial lesions as well as other rare miscellaneous lesions. They are challenging to categorise histologically, requiring specialist training and multidisciplinary input. They may coexist with in situ or invasive breast cancer (BC) and increase the risk of subsequent BC development. Management should focus on adequate classification and management whilst avoiding overtreatment. The aim of these guidelines is to provide updated information regarding the diagnosis and management of B3 lesions, according to updated literature review evidence.

METHODS

These guidelines provide practical recommendations which can be applied in clinical practice which include recommendation grade and level of evidence. All sections were written according to an updated literature review and discussed at a consensus meeting. Critical appraisal by the expert writing committee adhered to the 23 items in the international Appraisal of Guidelines, Research and Evaluation (AGREE) tool.

RESULTS

Recommendations for further management after core-needle biopsy (CNB) or vacuum-assisted biopsy (VAB) diagnosis of a B3 lesion reported in this guideline, vary depending on the presence of atypia, size of lesion, sampling size, and patient preferences. After CNB or VAB, the option of vacuum-assisted excision or surgical excision should be evaluated by a multidisciplinary team and shared decision-making with the patient is crucial for personalizing further treatment. De-escalation of surgical intervention for B3 breast lesions is ongoing, and the inclusion of vacuum-assisted excision (VAE) will decrease the need for surgical intervention in further approaches. Communication with patients may be different according to histological diagnosis, presence or absence of atypia, or risk of upgrade due to discordant imaging. Written information resources to help patients understand these issues alongside with verbal communication is recommended. Lifestyle interventions have a significant impact on BC incidence so lifestyle interventions need to be suggested to women at increased BC risk as a result of a diagnosis of a B3 lesion.

CONCLUSIONS

These guidelines provide a state-of-the-art overview of the diagnosis, management and prognosis of B3 lesions in modern multidisciplinary breast practice.

Updates in the Use of Immunohistochemical Stains in Breast and Gynecologic Pathology

CONTEXT.—

The use of immunohistochemical stains in breast and gynecologic pathology has become increasingly complex, with various diagnostic, prognostic, and predictive applications.

OBJECTIVE.—

To provide an update and review of immunohistochemical stains used in the practice of breast and gynecologic pathology. Established and new entities are reviewed, with descriptions of histomorphology and immunohistochemical staining patterns and discussion of interpretive pitfalls.

DATA SOURCES.—

Data were obtained from review of the English-language literature and firsthand experience of the authors in breast and gynecologic pathology.

CONCLUSIONS.—

Many entities in breast and gynecologic pathology benefit from evaluation with various immunohistochemical stains. These studies not only aid in the diagnosis and staging of tumors but also can provide prognostic and predictive information. Updated guidelines for recommended ancillary studies such as mismatch repair, p53, and human epidermal growth factor receptor 2 (HER2) studies in endometrium, as well as estrogen and progesterone receptors and HER2 in breast, are discussed. Finally, the use and interpretation of established and novel immunohistochemical stains are discussed in various breast and gynecologic malignancies.

Canonical Kaiso target genes define a functional signature that associates with breast cancer survival and the invasive lobular carcinoma histological type

Invasive lobular carcinoma (ILC) is a low- to intermediate-grade histological breast cancer type caused by mutational inactivation of E-cadherin function, resulting in the acquisition of anchorage independence (anoikis resistance). Most ILC cases express estrogen receptors, but options are limited in relapsed endocrine-refractory disease as ILC tends to be less responsive to standard chemotherapy. Moreover, ILC can relapse after >15 years, an event that currently cannot be predicted. E-cadherin inactivation leads to p120-catenin-dependent relief of the transcriptional repressor Kaiso (ZBTB33) and activation of canonical Kaiso target genes. Here, we examined whether an anchorage-independent and ILC-specific transcriptional program correlated with clinical parameters in breast cancer. Based on the presence of a canonical Kaiso-binding consensus sequence (cKBS) in the promoters of genes that are upregulated under anchorage-independent conditions, we defined an ILC-specific anoikis resistance transcriptome (ART). Converting the ART genes into human orthologs and adding published Kaiso target genes resulted in the Kaiso-specific ART (KART) 33-gene signature, used subsequently to study correlations with histological and clinical variables in primary breast cancer. Using publicly available data for ERPOS Her2NEG breast cancer, we found that expression of KART was positively associated with the histological ILC breast cancer type (p < 2.7E-07). KART expression associated with younger patients in all invasive breast cancers and smaller tumors in invasive ductal carcinoma of no special type (IDC-NST) (<2 cm, p < 6.3E-10). We observed associations with favorable long-term prognosis in both ILC (hazard ratio [HR] = 0.51, 95% CI = 0.29-0.91, p < 3.4E-02) and IDC-NST (HR = 0.79, 95% CI = 0.66-0.93, p < 1.2E-04). Our analysis thus defines a new mRNA expression signature for human breast cancer based on canonical Kaiso target genes that are upregulated in E-cadherin deficient ILC. The KART signature may enable a deeper understanding of ILC biology and etiology. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Lobular Carcinoma of the Breast: A Comprehensive Review with Translational Insights

The second most common breast carcinoma, invasive lobular carcinoma, accounts for approximately 15% of tumors of breast origin. Its incidence has increased in recent times due in part to hormone replacement therapy and improvement in diagnostic modalities. Although believed to arise from the same cell type as their ductal counterpart, invasive lobular carcinomas (ILCs) are a distinct entity with different regulating genetic pathways, characteristic histologies, and different biology. The features most unique to lobular carcinomas include loss of E-Cadherin leading to discohesion and formation of a characteristic single file pattern on histology. Because most of these tumors exhibit estrogen receptor positivity and Her2 neu negativity, endocrine therapy has predominated to treat these tumors. However novel treatments like CDK4/6 inhibitors have shown importance and antibody drug conjugates may be instrumental considering newer categories of Her 2 Low breast tumors. In this narrative review, we explore multiple pathological aspects and translational features of this unique entity. In addition, due to advancement in technologies like spatial transcriptomics and other hi-plex technologies, we have tried to enlist upon the characteristics of the tumor microenvironment and the latest associated findings to better understand the new prospective therapeutic options in the current era of personalized treatment.

Immunohistochemistry in the Diagnosis and Classification of Breast Tumors

CONTEXT.—

In the clinical practice of breast pathology, immunohistochemistry (IHC) of different markers is widely used for the diagnosis and classification of breast lesions.

OBJECTIVE.—

To provide an overview of currently used and recently identified IHC stains that have been implemented in the field of diagnostic breast pathology.

DATA SOURCES.—

Data were obtained from literature review and clinical experience of the authors as breast pathologists.

CONCLUSIONS.—

In the current review, we summarize the common uses of IHC stains for diagnosing different types of breast lesions, especially invasive and noninvasive breast lesions, and benign and malignant spindle cell lesions. In addition, the cutting-edge knowledge of diagnostic carcinoma markers will lead us to further understand the different types of breast carcinoma and differentiate breast carcinomas from other carcinomas of similar morphology. Knowing the strengths and limitations of these markers is essential to the clinical practice of breast pathology.

Clinicopathologic and genomic features of lobular like invasive mammary carcinoma: is it a distinct entity?

This study describes "lobular-like invasive mammary carcinomas" (LLIMCas), a group of low- to intermediate-grade invasive mammary carcinomas with discohesive, diffusely infiltrative cells showing retained circumferential membranous immunoreactivity for both E-cadherin and p120. We analyzed the clinical-pathologic features of 166 LLIMCas compared to 104 classical invasive lobular carcinomas (ILCs) and 100 grade 1 and 2 invasive ductal carcinomas (IDCs). Tumor size and pT stage of LLIMCas were intermediate between IDCs and ILCs, and yet often underestimated on imaging and showed frequent positive margins on the first resection. Despite histomorphologic similarities to classical ILC, the discohesion in LLIMCa was independent of E-cadherin/p120 immunophenotypic alteration. An exploratory, hypothesis-generating analysis of the genomic features of 14 randomly selected LLIMCas and classical ILCs (7 from each category) was performed utilizing an FDA-authorized targeted capture sequencing assay (MSK-IMPACT). None of the seven LLIMCas harbored CDH1 loss-of-function mutations, and none of the CDH1 alterations detected in two of the LLIMCas was pathogenic. In contrast, all seven ILCs harbored CDH1 loss-of-function mutations coupled with the loss of heterozygosity of the CDH1 wild-type allele. Four of the six evaluable LLIMCas were positive for CDH1 promoter methylation, which may partially explain the single-cell infiltrative morphology seen in LLIMCa. Further studies are warranted to better define the molecular basis of the discohesive cellular morphology in LLIMCa. Until more data becomes available, identifying LLIMCas and distinguishing them from typical IDCs and ILCs would be justified. In patients with LLIMCas, preoperative MRI should be entertained to guide surgical management.

FDG and Non-FDG Radiopharmaceuticals for PET Imaging in Invasive Lobular Breast Carcinoma

Invasive lobular cancer (ILC) is the second most frequent histological type of breast cancer (BC) and includes a heterogeneous spectrum of diseases with unique characteristics, especially the infiltrative growth pattern and metastatic spread. [¹⁸F]fluoro-2-deoxy-D-glucose positron emission tomography/computed tomography (FDG-PET/CT) is extensively used in oncology and BC patient evaluation. Its role in ILCs is considered suboptimal due to its low FDG avidity. Therefore, ILCs could benefit from molecular imaging with non-FDG tracers that target other specific pathways, contributing to precision medicine. This narrative review aims to summarize the current literature on the use of FDG-PET/CT in ILC and to discuss future opportunities given by the development of innovative non-FDG radiotracers.

Mixed invasive ductal lobular carcinoma is clinically and pathologically more similar to invasive lobular than ductal carcinoma

BACKGROUND

Mixed invasive ductal lobular carcinoma (mDLC) remains a poorly understood subtype of breast cancer composed of coexisting ductal and lobular components.

METHODS

We sought to describe clinicopathologic characteristics and determine whether mDLC is clinically more similar to invasive ductal carcinoma (IDC) or invasive lobular carcinoma (ILC), using data from patients seen at the University of Pittsburgh Medical Center.

RESULTS

We observed a higher concordance in clinicopathologic characteristics between mDLC and ILC, compared to IDC. There is a trend for higher rates of successful breast-conserving surgery after neoadjuvant chemotherapy in patients with mDLC compared to patients with ILC, in which it is known to be lower than in those with IDC. Metastatic patterns of mDLC demonstrate a propensity to develop in sites characteristic of both IDC and ILC. A meta-analysis evaluating mDLC showed shared features with both ILC and IDC with significantly more ER-positive and fewer high grades in mDLC compared to IDC, although mDLCs were significantly smaller and included fewer late-stage tumours compared to ILC.

CONCLUSIONS

These findings support clinicopathologic characteristics of mDLC driven by individual ductal vs lobular components and given the dominance of lobular pathology, mDLC features are often more similar to ILC than IDC. This study exemplifies the complexity of mixed disease.

Pitfalls in breast pathology

Accurate pathological diagnosis is the cornerstone of optimal clinical management for patients with breast disease. As non-operative diagnosis has now become the standard of care, histopathologists encounter the daily challenge of making definitive diagnoses on limited breast core needle biopsy (CNB) material. CNB samples are carefully evaluated using microscopic examination of haematoxylin and eosin (H&E)-stained slides and supportive immunohistochemistry (IHC), providing the necessary information to inform the next steps in the patient care pathway. Some entities may be difficult to distinguish on small tissue samples, and if there is uncertainty a diagnostic excision biopsy should be recommended. This review discusses (1) benign breast lesions that may mimic malignancy, (2) malignant conditions that may be misinterpreted as benign, (3) malignant conditions that may be incorrectly diagnosed as primary breast carcinoma, and (4) some IHC pitfalls. The aim of the review is to raise awareness of potential pitfalls in the interpretation of breast lesions that may lead to underdiagnosis, overdiagnosis, or incorrect classification of malignancy with potential adverse outcomes for individual patients.

The morphologic spectrum of lobular carcinoma in situ (LCIS) observations on clinical significance, management implications and diagnostic pitfalls of classic, florid and pleomorphic LCIS

Lobular carcinoma in situ (LCIS) is a non-invasive proliferation of atypical dyscohesive epithelial cells characterized by loss or functional alteration of E-cadherin-mediated cell adhesion. The morphologic spectrum of LCIS encompasses classic (C-LCIS), florid (F-LCIS) and pleomorphic LCIS (P-LCIS), as recently defined by the World Health Organization (WHO) Expert Consensus Group. Atypical lobular hyperplasia (ALH) is also part of this spectrum.This article highlights the morphologic and immunohistochemical features of the three forms of LCIS and summarizes their management implications and prognosis, with emphasis on F-LCIS and P-LCIS.

Avoiding "False Positive" and "False Negative" Immunohistochemical Results in Breast Pathology

Immunohistochemistry (IHC) plays an important role in the evaluation of breast pathology specimens to provide both diagnostic and prognostic/therapeutic information. Although most IHCs used in breast pathology can be easily interpreted, pitfalls do exist, especially in some uncommon scenarios. This review intends to focus on the challenging areas such as the interpretation of myoepithelial cell markers in differentiating benign proliferation and in situ carcinoma from invasive carcinoma, lobular cell markers in differentiating lobular from ductal carcinoma, cytokeratin and other markers in diagnosing metaplastic carcinoma, and breast tissue origin markers in diagnosing breast primary carcinoma. The challenges in interpreting prognostic and predictive markers will be also discussed.

Inter-observer agreement for the histological diagnosis of invasive lobular breast carcinoma

Invasive lobular breast carcinoma (ILC) is the second most common breast carcinoma (BC) subtype and is mainly driven by loss of E‐cadherin expression. Correct classification of BC as ILC is important for patient treatment. This study assessed the degree of agreement among pathologists for the diagnosis of ILC. Two sets of hormone receptor (HR)‐positive/HER2‐negative BCs were independently reviewed by participating pathologists. In set A (61 cases), participants were provided with hematoxylin/eosin (HE)‐stained sections. In set B (62 cases), participants were provided with HE‐stained sections and E‐cadherin immunohistochemistry (IHC). Tumor characteristics were balanced. Participants classified specimens as non‐lobular BC versus mixed BC versus ILC. Pairwise inter‐observer agreement and agreement with a pre‐defined reference diagnosis were determined with Cohen's kappa statistics. Subtype calls were correlated with molecular features, including CDH1/E‐cadherin mutation status. Thirty‐five pathologists completed both sets, providing 4,305 subtype calls. Pairwise inter‐observer agreement was moderate in set A (median κ = 0.58, interquartile range [IQR]: 0.48–0.66) and substantial in set B (median κ = 0.75, IQR: 0.56–0.86, p < 0.001). Agreement with the reference diagnosis was substantial in set A (median κ = 0.67, IQR: 0.57–0.75) and almost perfect in set B (median κ = 0.86, IQR: 0.73–0.93, p < 0.001). The median frequency of CDH1/E‐cadherin mutations in specimens classified as ILC was 65% in set A (IQR: 56–72%) and 73% in set B (IQR: 65–75%, p < 0.001). Cases with variable subtype calls included E‐cadherin‐positive ILCs harboring CDH1 missense mutations, and E‐cadherin‐negative ILCs with tubular elements and focal P‐cadherin expression. ILCs with trabecular growth pattern were often misclassified as non‐lobular BC in set A but not in set B. In conclusion, subtyping of BC as ILC achieves almost perfect agreement with a pre‐defined reference standard, if assessment is supported by E‐cadherin IHC. CDH1 missense mutations associated with preserved E‐cadherin protein expression, E‐ to P‐cadherin switching in ILC with tubular elements, and trabecular ILC were identified as potential sources of discordant classification.

Special Histologic Type and Rare Breast Tumors - Diagnostic Review and Clinico-Pathological Implications

Breast cancer is the most common malignant tumor in females. While most carcinomas are categorized as invasive carcinoma, no special type (NST), a diverse group of tumors with distinct pathologic and clinical features is also recognized, ranging in incidence from relatively more common to rare. So-called "special histologic type" tumors display more than 90% of a specific, distinctive histologic pattern, while a spectrum of tumors more often encountered in the salivary gland may also arise in the breast. Metaplastic carcinomas can present diagnostic challenges. Some uncommon tumors harbor pathognomonic genetic alterations. This article provides an overview of the key diagnostic points and differential diagnoses for this group of disparate lesions, as well as the salient clinical characteristics of each entity.

Assessment of the Molecular Heterogeneity of E-Cadherin Expression in Invasive Lobular Breast Cancer

Simple Summary

Invasive lobular breast cancers (ILCs) are histologically classified by their discohesive growth pattern, due to loss of the cell adhesion glycoprotein E-cadherin (CDH1), which arises via mutation in CDH1 in around half of these tumours. A subset of these tumours, however, show mixed levels of E-cadherin expression. Here, we sought to address whether the distinct parts of individual tumours showing heterogeneous E-cadherin expression harbour distinct driver alterations. Using whole genome sequencing and methylation profiling of nine such cases, we identified that these tumours are clonally related, suggesting that they are part of the spectrum of ILC tumours. CDH1 mutant tumours showed a higher mutational burden indicative of APOBEC-mediated mutagenesis. In some cases, known clinically actionable driver mutations, such as PIK3CA, were exclusive to one component. Together, these results highlight the heterogeneity underpinning this special histological breast cancer.

Abstract

Mutations and loss of E-cadherin protein expression define the vast majority of invasive lobular carcinomas. In a subset of these cases, the heterogeneous expression of E-cadherin is observed either as wild-type (strong membranous) expression or aberrant expression (cytoplasmic expression). However, it is unclear as to whether the two components would be driven by distinct genetic or epigenetic alterations. Here, we used whole genome DNA sequencing and methylation array profiling of two separately dissected components of nine invasive lobular carcinomas with heterogeneous E-cadherin expression. E-cadherin negative and aberrant/positive components of E-cadherin heterogeneous tumours showed a similar mutational, copy number and promoter methylation repertoire, suggesting they arise from a common ancestor, as opposed to the collision of two independent tumours. We found that the majority of E-cadherin heterogeneous tumours harboured CDH1 mutations in both the E-cadherin negative and aberrant/positive components together with somatic mutations in additional driver genes known to be enriched in both pure invasive carcinomas of no special type and invasive lobular breast cancers, whereas these were less commonly observed in CDH1 wild-type tumours. CDH1 mutant tumours also exhibited a higher mutation burden as well as increased presence of APOBEC-dependent mutational signatures 2 and 13 compared to CDH1 wild-type tumours. Together, our results suggest that regardless of E-cadherin protein expression, tumours showing heterogeneous expression of E-cadherin should be considered as part of the spectrum of invasive lobular breast cancers.

Results of a worldwide survey on the currently used histopathological diagnostic criteria for invasive lobular breast cancer

Invasive lobular carcinoma (ILC) represents the second most common subtype of breast cancer (BC), accounting for up to 15% of all invasive BC. Loss of cell adhesion due to functional inactivation of E-cadherin is the hallmark of ILC. Although the current world health organization (WHO) classification for diagnosing ILC requires the recognition of the dispersed or linear non-cohesive growth pattern, it is not mandatory to demonstrate E-cadherin loss by immunohistochemistry (IHC). Recent results of central pathology review of two large randomized clinical trials have demonstrated relative overdiagnosis of ILC, as only ~60% of the locally diagnosed ILCs were confirmed by central pathology. To understand the possible underlying reasons of this discrepancy, we undertook a worldwide survey on the current practice of diagnosing BC as ILC. A survey was drafted by a panel of pathologists and researchers from the European lobular breast cancer consortium (ELBCC) using the online tool SurveyMonkey®. Various parameters such as indications for IHC staining, IHC clones, and IHC staining procedures were questioned. Finally, systematic reporting of non-classical ILC variants were also interrogated. This survey was sent out to pathologists worldwide and circulated from December 14, 2020 until July, 1 2021. The results demonstrate that approximately half of the institutions use E-cadherin expression loss by IHC as an ancillary test to diagnose ILC and that there is a great variability in immunostaining protocols. This might cause different staining results and discordant interpretations. As ILC-specific therapeutic and diagnostic avenues are currently explored in the context of clinical trials, it is of importance to improve standardization of histopathologic diagnosis of ILC diagnosis.

New variant of breast-invasive lobular carcinoma with solid and encapsulated papillary carcinoma growth pattern

To date, five cases of invasive lobular carcinoma with solid and encapsulated papillary carcinoma (SPC and EPC) growth pattern were reported. In this article, we describe such a case that might represent a diagnostic pitfall. A 61-year-old woman had a mass on the left breast that was characterized by multiple expansile nodules with a fibrous capsule. Tumor cells were arranged in a solid pattern with inconspicuous delicate fibrovascular cores, some were irregular glandular tubes and papillary, similar to the growth pattern of SPC and EPC. The appearance of the tumor surrounding tissue suggested a special type of lobular carcinoma. The diagnosis of invasive lobular carcinoma was confirmed by immunohistochemistry, which revealed negative E-cadherin, positive cytoplasmic P120, and deleted myoepithelium. Next-generation sequencing revealed CDH1 mutations that further proved the diagnosis of invasive lobular carcinoma. The main differential diagnoses for this tumor are SPC, EPC, neuroendocrine carcinoma, and secretory carcinoma, for which immunohistochemical analysis is an essential diagnostic tool. The growth pattern of invasive lobular carcinoma with EPC and SPC is a variant of the invasive lobular carcinoma newly discovered. The understanding of this variant expands the morphological spectrum of invasive lobular carcinoma and will help prevent misdiagnosis.

Lobular Breast Cancer: Histomorphology and Different Concepts of a Special Spectrum of Tumors

Simple Summary

Invasive lobular breast cancer (ILC) is a special type of breast cancer (BC) that was first described in 1941. The diagnosis of ILC is made by microscopy of tumor specimens, which reveals a distinct morphology. This review recapitulates the developments in the microscopic assessment of ILC from 1941 until today. We discuss different concepts of ILC, provide an overview on ILC variants, and highlight advances which have contributed to a better understanding of ILC as a special histologic spectrum of tumors.

Abstract

Invasive lobular breast cancer (ILC) is the most common special histological type of breast cancer (BC). This review recapitulates developments in the histomorphologic assessment of ILC from its beginnings with the seminal work of Foote and Stewart, which was published in 1941, until today. We discuss different concepts of ILC and their implications. These concepts include (i) BC arising from mammary lobules, (ii) BC growing in dissociated cells and single files, and (iii) BC defined as a morpho-molecular spectrum of tumors with distinct histological and molecular characteristics related to impaired cell adhesion. This review also provides a comprehensive overview of ILC variants, their histomorphology, and differential diagnosis. Furthermore, this review highlights recent advances which have contributed to a better understanding of the histomorphology of ILC, such as the role of the basal lamina component laminin, the molecular specificities of triple-negative ILC, and E-cadherin to P-cadherin expression switching as the molecular determinant of tubular elements in CDH1-deficient ILC. Last but not least, we provide a detailed account of the tumor microenvironment in ILC, including tumor infiltrating lymphocyte (TIL) levels, which are comparatively low in ILC compared to other BCs, but correlate with clinical outcome. The distinct histomorphology of ILC clearly reflects a special tumor biology. In the clinic, special treatment strategies have been established for triple-negative, HER2-positive, and ER-positive BC. Treatment specialization for patients diagnosed with ILC is just in its beginnings. Accordingly, ILC deserves greater attention as a special tumor entity in BC diagnostics, patient care, and cancer research.

Why is LCIS Important—Pathological Review

Purpose of Review

Lobular carcinoma in situ (LCIS) encompasses classical LCIS and other rarer and more recently recognised variants, namely pleomorphic LCIS (PLCIS) and florid LCIS. Each of those entities has characteristic histological diagnostic criteria, different rates of underestimation of malignancy and recommended management. In addition, those lesions can mimic a number of benign and malignant breast lesions and can particularly be mistaken for ductal carcinoma in situ (DCIS). Accurate diagnosis of those lesions is critical to ensuring the appropriate patient management.

Recent Findings

Several international guidelines refining the pathological classification, staging and management of those lesions have recently been updated. This review will provide an up-to-date pathological overview of the current knowledge of LCIS with emphasis on the multidisciplinary management implications.

Summary

Close correlation between imaging and pathology in a multidisciplinary pathway is essential in LCIS management. Classical LCIS on core biopsy/vacuum-assisted biopsy (VAB) is coded as B3 and, if without discordant imaging, should further be sampled by vacuum-assisted excision (VAE). PLCIS should be coded and managed as per high-grade DCIS. Florid LCIS is a rare entity that is thought to be more aggressive than classical LCIS. Excision with clear margin is advised.

Comprehensive Review of Molecular Mechanisms and Clinical Features of Invasive Lobular Cancer

Invasive lobular carcinoma (ILC) accounts for 10% to 15% of breast cancers in the United States, 80% of which are estrogen receptor (ER)-positive, with an unusual metastatic pattern of spread to sites such as the serosa, meninges, and ovaries, among others. Lobular cancer presents significant challenges in detection and clinical management given its multifocality and multicentricity at presentation. Despite the unique features of ILC, it is often lumped with hormone receptor-positive invasive ductal cancers (IDC); consequently, ILC screening, treatment, and follow-up strategies are largely based on data from IDC. Despite both being treated as ER-positive breast cancer, querying the Cancer Genome Atlas database shows distinctive molecular aberrations in ILC compared with IDC, such as E-cadherin loss (66% vs. 3%), FOXA1 mutations (7% vs. 2%), and GATA3 mutations (5% vs. 20%). Moreover, compared with patients with IDC, patients with ILC are less likely to undergo breast-conserving surgery, with lower rates of complete response following therapy as these tumors are less chemosensitive. Taken together, this suggests that ILC is biologically distinct, which may influence tumorigenesis and therapeutic strategies. Long-term survival and clinical outcomes in patients with ILC are worse than in stage- and grade-matched patients with IDC; therefore, nuanced criteria are needed to better define treatment goals and protocols tailored to ILC's unique biology. This comprehensive review highlights the histologic and clinicopathologic features that distinguish ILC from IDC, with an in-depth discussion of ILC's molecular alterations and biomarkers, clinical trials and treatment strategies, and future targets for therapy. IMPLICATIONS FOR PRACTICE: The majority of invasive lobular breast cancers (ILCs) are hormone receptor (HR)-positive and low grade. Clinically, ILC is treated similar to HR-positive invasive ductal cancer (IDC). However, ILC differs distinctly from IDC in its clinicopathologic characteristics and molecular alterations. ILC also differs in response to systemic therapy, with studies showing ILC as less sensitive to chemotherapy. Patients with ILC have worse clinical outcomes with late recurrences. Despite these differences, clinical trials treat HR-positive breast cancers as a single disease, and there is an unmet need for studies addressing the unique challenges faced by patients diagnosed with ILC.

p-120 Catenin is a Useful Diagnostic Biomarker for Distinguishing Plasmacytoid and Sarcomatoid Variants From Conventional Urothelial Carcinoma

CONTEXT.—

Plasmacytoid urothelial carcinoma (PC-UC) is an aggressive variant of urothelial carcinoma (UC), characterized by loss of E-cadherin (E-Cad)-mediated intercellular adhesion. Loss of E-Cad by immunohistochemistry can help diagnose PC-UC; however, sensitivity is limited. Expression of other cadherin-catenin adhesion complex members, that is, p-120 catenin (p-120) and β-catenin (B-Cat), which are diagnostically useful for lobular breast carcinoma, remains unknown in UC.

OBJECTIVE.—

To determine the utility of p-120 and B-Cat in conventional and variant UC.

DESIGN.—

E-cadherin, B-Cat, and p-120 immunohistochemistry was performed in 25 conventional UCs and 33 variant UCs, including 22 PC-UCs, 6 sarcomatoid UCs (SUCs), and 5 micropapillary UCs. Membranous staining for all biomarkers was considered normal; however, any cytoplasmic staining or an absence of staining was considered diagnostically abnormal. Next-generation sequencing was performed on 8 PC-UC cases.

RESULTS.—

E-cadherin, B-Cat, and p-120 showed membranous staining in all conventional and micropapillary UCs. In contrast, most PC-UCs were negative for E-Cad (17 of 22; 77%) with an additional 2 of 22 cases (9%) showing cytoplasmic with partial membranous staining. p-120 catenin demonstrated cytoplasmic or negative staining in 21 of 22 cases (95%). Most SUCs showed an absence of E-Cad (5 of 6; 83%) and cytoplasmic or negative p-120 in 5 of 6 cases (83%). Staining for B-Cat was also abnormal in a subset of PC-UCs and SUCs. Five PC-UC cases that harbored CDH1 gene variants were p-120 cytoplasmic positive.

CONCLUSIONS.—

p-120 catenin is a useful adjunct biomarker to E-Cad in the clinically important distinction of PC-UC and SUC from conventional UC. In particular, the combination of cytoplasmic p-120 and loss of E-Cad is strongly supportive of PC-UC and SUC.

Invasive plasmacytoid urothelial carcinoma: A comparative study of E-cadherin and P120 catenin

Invasive plasmacytoid urothelial carcinomas (PUCs) are an uncommon aggressive variant, which often shows immunohistochemical loss of E-cadherin, underlying its distinct discohesive histology. The marker P120 (well described in breast pathology as being a diagnostic tool alongside E-cadherin for lobular neoplasia) has not been evaluated in PUCs. Biopsies, transurethral resections, and cystectomies of PUCs were collected, and whole-slide immunohistochemical analysis of E-cadherin and P120 was applied. A subset of cases were also tested for CDH1 mutation. PUC cases were stratified into morphologic categories of classic, pleomorphic, or desmoplastic. For E-cadherin, 24 of 33 (73%) cases showed an abnormal staining pattern, consisting of complete absence of staining (17/24; 71%) or cytoplasmic staining (7/24; 29%). For P120, 24 of 33 (73%) cases showed an abnormal staining pattern, consisting of loss of membranous staining with cytoplasmic reactivity. Only 2 cases showed a discordant E-cadherin/P120 immunoprofile (94% concordance). Significant staining differences among the 3 morphologic categories were not found. CDH1 mutation was found in 4 of 8 (50%) of cases, with 3 of 4 (75%) cases showing matched molecular/immunoprofile reactivity. No cases with CDH1 mutation showed discordant pattern E-cadherin/P120 immunoreactivity. Our rate of aberrant E-cadherin immunoreactivity in PUCs (73%) is similar to a meta-analysis of published cases (74%). We also report an identical rate of aberrant P120 immunoreactivity in PUCs (73%). While PUC remains a histologic diagnosis, in a subset of cases showing a less appreciated pattern (such as desmoplastic) or confounding cytoplasmic E-cadherin reactivity, the utility of paired P120 staining may be a useful diagnostic tool.

E-cadherin immunohistochemical expression in invasive lobular carcinoma of the breast: correlation with morphology and CDH1 somatic alterations

E-cadherin (ECAD) immunohistochemical (IHC) expression is lost in ∼90% of invasive lobular carcinomas (ILCs) owing to genomic alterations of CDH1. We examined morphologic features and ECAD IHC expression in invasive breast carcinomas (BCs) with known CDH1 alterations. Between January 2014 and May 2018, 202 cases of BC with a CDH1 somatic alteration were identified. ECAD expression was lost in 77% (155/202) of cases and was retained in 23% (47/202) cases. Most (90%, 139/155) ECAD-negative cases were morphologically classified as ILC, while the remaining (10%, 16/155) were invasive mammary carcinoma with mixed ductal and lobular features (IMC). Of 47 cases with ECAD staining, 62% (29/47) were classified as ILC, 23% (11/47) were classified as IMC, and 15% (7/47) were classified as invasive ductal carcinoma (IDC). Of note, 51% (24/47) of ECAD-positive cases were initially diagnosed as IDC or IMC based on ECAD expression alone. For ECAD-negative BCs, 98% (152/155) of CDH1 alterations were truncating, and 2% (3/155) were variants of unknown significance (VUS). Truncating CDH1 alterations were identified in the majority of ECAD-positive BCs (72%, 34/47); however, VUS-type CDH1 alterations were more prevalent (28%, 13/47) in ECAD-positive BCs than in ECAD-negative BCs. Although 90% of ECAD-negative tumors were compatible with ILC in this study, 17% (29/168) of ILC cases were ECAD positive. In addition, CDH1 truncating alterations were seen in ECAD-positive ILC, supporting the notion of aberrant ECAD staining. Therefore, ECAD IHC expression must be interpreted in conjunction with morphology, and BC with classic histologic features of ILC should not be reclassified as IDC/IMC based solely on the status of ECAD IHC expression.

Non-invasive lobular neoplasia of the breast: Morphologic features, clinical presentation, and management dilemmas

The designation of noninvasive lobular neoplasia applies to atypical epithelial proliferations composed of noncohesive cells secondary to loss or functional alteration of E-cadherin-mediated cell adhesion. The morphologic spectrum of noninvasive lobular neoplasia encompasses atypical lobular hyperplasia (ALH) and classic lobular carcinoma in situ (classic LCIS) and two LCIS variants, namely florid LCIS (F-LCIS) and pleomorphic LCIS (P-LCIS), as defined in the World Health Organization (WHO) Classification of Tumors of the Breast 5th ed. Herein, we review the morphologic, immunohistochemical, and molecular features of noninvasive lobular neoplasia, with special emphasis on F-LCIS and P-LCIS. We also review imaging features, management at core needle biopsy, upgrade rates at surgical excision, and clinical management dilemmas.

Invasive Lobular Breast Cancer as a Distinct Disease: Implications for Therapeutic Strategy

Invasive lobular carcinoma comprises 10-15% of all breast cancers and is increasingly recognised as a distinct and understudied disease compared with the predominant histological subtype, invasive ductal carcinoma. Hallmarks of invasive lobular carcinoma include E-cadherin loss, leading to discohesive morphology with cells proliferating in single-file strands and oestrogen receptor positivity, with favourable response to endocrine therapy. This review summarises the distinct histological and molecular features of invasive lobular carcinoma with focus on diagnostic challenges and the impact on surgical management and medical therapy. Emphasis is placed on recent advances in our understanding of the unique molecular biology of lobular breast cancer and how this is optimising our therapy approach in the clinic.

Immunohistochemistry for diagnosis and prognosis of breast cancer: a review

Breast cancer is the most prevalent malignant tumor and main oncologic cause of mortality in women. Although most diagnosis of breast pathology is accomplished using hematoxylin and eosin stained sections, some cases require immunohistochemistry for proper evaluation. We investigated the latter cases including distinctions between ductal and lobular carcinoma, in situ and invasive carcinoma, typical ductal hyperplasia and atypical ductal hyperplasia/ductal carcinoma in situ, papillary and spindle cell lesion assessment, metastasis evaluation, and assessment of prognostic and therapy markers. E-cadherin is used to differentiate ductal and lobular carcinoma; 34βE12, CK8, p120 catenin and β-catenin also produce consistent results. Myoepithelial cell (MEC) stains are used to evaluate in situ and invasive carcinoma; calponin, smooth muscle myosin heavy chain and p63 are sensitive/specific markers. 34βE12 and CK5/6 are positive in ductal hyperplasia, which enables its differentiation from atypical ductal hyperplasia and ductal carcinoma in situ. CK 5/6, ER and MEC markers are consistent options for evaluating papillary lesions. Spindle cell lesions can be assessed using β-catenin, SMA, CD34, p63, CKs and hormone receptors. It is important to differentiate primary carcinomas from metastases; the most commonly used markers to identify breast origin include mammaglobin, GCDFP-15, GATA3 and ER, although none of these is completely sensitive or specific. Immunohistochemistry can be used to evaluate central prognostic and predictive factors including molecular subtypes, HER2, hormone receptors, proliferation markers (Ki-67) and lymph-vascular invasion markers including ERG, CD31, CD34, factor VIII and podoplanin. Owing to the complexity of mammary lesions, diagnosis also depends on each particular situation, evaluation of cytological characteristics revealed by immunochemistry and correlation with histological findings.

Invasive lobular breast cancer: A review of pathogenesis, diagnosis, management, and future directions of early stage disease

Invasive lobular carcinoma (ILC) is the second most common type of invasive breast cancer after invasive ductal carcinoma (IDC). Invasive lobular carcinoma has unique clinical, pathologic, and radiographic features which suggest that it is a distinct clinical entity; however, it is treated with the same treatment paradigms as IDC. Information regarding the specific treatment of ILC, including response to standard therapy, is sparse. Neoadjuvant treatment considerations are of great importance in this space as ILC is often found at a locally advanced stage. In this review, we summarize the classic features of ILC and the available data regarding efficacy of both endocrine therapy and chemotherapy in curative treatment of breast cancer.

Mixed Invasive Ductal and Lobular Carcinoma of the Breast: Prognosis and the Importance of Histologic Grade

BACKGROUND

The diagnosis of mixed invasive ductal and lobular carcinoma (IDC-L) in clinical practice is often associated with uncertainty related to its prognosis and response to systemic therapies. With the increasing recognition of invasive lobular carcinoma (ILC) as a distinct disease subtype, questions surrounding IDC-L become even more relevant. In this study, we took advantage of a detailed clinical database to compare IDC-L and ILC regarding clinicopathologic and treatment characteristics, prognostic power of histologic grade, and survival outcomes.

MATERIALS AND METHODS

In this retrospective cohort study, we identified 811 patients diagnosed with early-stage breast cancer with IDC-L or ILC. Descriptive statistics were performed to compare baseline clinicopathologic characteristics and treatments. Survival rates were subsequently analyzed using the Kaplan-Meier method and compared using the Cox proportional hazards model.

RESULTS

Patients with ILC had more commonly multifocal disease, low to intermediate histologic grade, and HER2-negative disease. Histologic grade was prognostic for patients with IDC-L but had no significant discriminatory power in patients with ILC. Among postmenopausal women, those with IDC-L had significantly better outcomes when compared with those with ILC: disease-free survival (DFS) and overall survival (OS; adjusted hazard ratio [HR], 0.54; 95% confidence interval [CI] 0.31-0.95). Finally, postmenopausal women treated with an aromatase inhibitor had more favorable DFS and OS than those treated with tamoxifen only (OS adjusted HR, 0.50; 95% CI, 0.29-0.87), which was similar for both histologic types (p = .212).

CONCLUSION

IDC-L tumors have a better prognosis than ILC tumors, particularly among postmenopausal women. Histologic grade is an important prognostic factor in IDC-L but not in ILC.

IMPLICATIONS FOR PRACTICE

This study compared mixed invasive ductal and lobular carcinoma (IDC-L) with invasive lobular carcinomas (ILCs) to assess the overall prognosis, the prognostic role of histologic grade, and response to systemic therapy. It was found that patients with IDC-L tumors have a better prognosis than ILC, particularly among postmenopausal women, which may impact follow-up strategies. Moreover, although histologic grade failed to stratify the risk of ILC, it showed an important prognostic power in IDC-L, thus highlighting its clinical utility to guide treatment decisions of IDC-L. Finally, the disease-free survival advantage of adjuvant aromatase inhibitors over tamoxifen in ILC was consistent in IDC-L.

E-cadherin loss induces targetable autocrine activation of growth factor signalling in lobular breast cancer

Despite the fact that loss of E-cadherin is causal to the development and progression of invasive lobular carcinoma (ILC), options to treat this major breast cancer subtype are limited if tumours develop resistance to anti-oestrogen treatment regimens. This study aimed to identify clinically targetable pathways that are aberrantly active downstream of E-cadherin loss in ILC. Using a combination of reverse-phase protein array (RPPA) analyses, mRNA sequencing, conditioned medium growth assays and CRISPR/Cas9-based knock-out experiments, we demonstrate that E-cadherin loss causes increased responsiveness to autocrine growth factor receptor (GFR)-dependent activation of phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K)/Akt signalling. Autocrine activation of GFR signalling and its downstream PI3K/Akt hub was independent of oncogenic mutations in PIK3CA, AKT1 or PTEN. Analyses of human ILC samples confirmed growth factor production and pathway activity. Pharmacological inhibition of Akt using AZD5363 or MK2206 resulted in robust inhibition of cell growth and survival of ILC cells, and impeded tumour growth in a mouse ILC model. Because E-cadherin loss evokes hypersensitisation of PI3K/Akt activation independent of oncogenic mutations in this pathway, we propose clinical intervention of PI3K/Akt in ILC based on functional E-cadherin inactivation, irrespective of activating pathway mutations.

Re-Evaluating E-Cadherin and β-Catenin: A Pan-Cancer Proteomic Approach with an Emphasis on Breast Cancer

E-cadherin is conventionally considered to be a good prognostic marker in cancer. The loss of E-cadherin is one of the key hallmarks of epithelial-to-mesenchymal transition, a biological process that promotes cancer cell invasiveness and metastasis. Recent evidence has cast doubt on the importance of epithelial-to-mesenchymal transition in metastasis. The availability of protein-level data in the Cancer Genome Atlas allows for the quantitative analysis of protein and prognosis. The prognostic values of E-cadherin and β-catenin were revisited across 19 cancer types, and high E-cadherin was found to correlate with good prognosis in most cancers. Conversely, higher E-cadherin and β-catenin correlated with shorter survival in invasive breast carcinoma. Stratifying breast cancers by histologic subtype revealed that the poor prognosis of E-cadherin and β-catenin proteins was characteristic of infiltrating ductal, but not lobular, carcinomas. To further corroborate the protein findings and examine cellular localization, immunohistochemistry was used for E-cadherin and β-catenin in 163 breast patient samples from the Iowa cohort. Most previous studies showing that reduced or absent E-cadherin and β-catenin was inversely associated with tumor stages in ductal carcinomas were confirmed. Taken together, these results lead us to question the prognostic values of E-cadherin and β-catenin in ductal carcinomas and indicate a complicated role of E-cadherin and β-catenin in breast cancer progression.

Core Needle Biopsy of the Breast: An Evaluation of Contemporary Data

Benign and atypical lesions associated with breast cancer risk are often encountered in core needle biopsies (CNBs) of the breast. For these lesions, the rate of "upgrade" to carcinoma in excision specimens varies widely in the literature. Many CNB studies are limited by a lack of radiological-pathological correlation, consistent criteria for excision, and clinical follow-up for patients who forego excision. This article highlights contemporary diagnostic criteria and outcome data that would support an evidence-based approach to the management of these nonmalignant lesions of the breast diagnosed on CNB.

Loss of E-Cadherin-Dependent Cell-Cell Adhesion and the Development and Progression of Cancer

Classical cadherins are the key molecules that control cell-cell adhesion. Notwithstanding this function, it is also clear that classical cadherins are more than just the "glue" that keeps the cells together. Cadherins are essential regulators of tissue homeostasis that govern multiple facets of cellular function and development, by transducing adhesive signals to a complex network of signaling effectors and transcriptional programs. In cancer, cadherins are often inactivated or functionally inhibited, resulting in disease development and/or progression. This review focuses on E-cadherin and its causal role in the development and progression of breast and gastric cancer. We provide a summary of the biochemical consequences and consider the conceptual impact of early (mutational) E-cadherin loss in cancer. We advocate that carcinomas driven by E-cadherin loss should be considered "actin-diseases," caused by the specific disruption of the E-cadherin-actin connection and a subsequent dependence on sustained actomyosin contraction for tumor progression. Based on the available data from mouse and human studies we discuss opportunities for targeted clinical intervention.

Lobular Carcinoma In Situ

Lobular carcinoma in situ (LCIS) is a risk factor and a nonobligate precursor of breast carcinoma. The relative risk of invasive carcinoma after classic LCIS diagnosis is approximately 9 to 10 times that of the general population. Classic LCIS diagnosed on core biopsy with concordant imaging and pathologic findings does not mandate surgical excision, and margin status is not reported. The identification of variant LCIS in a needle core biopsy specimen mandates surgical excision, regardless of radiologic-pathologic concordance. The presence of variant LCIS close to the surgical margin of a resection specimen is reported, and reexcision should be considered.

Investigation of P120catenin Expression in Human Basal Cell Carcinoma of the Skin

BACKGROUND

P120(ctn) is a specific membranous adhesion protein, that maintains the stability of intercellular junctions. An altered expression of p120(ctn), either reduced in the cell membrane or increase in the cytoplasm, plays a crucial role in carcinogenesis. No research has analysed the expression of p120(ctn) in basal cell carcinoma (BCC) of the skin so far. Therefore, we immunohistochemically studied p120(ctn) in a set of cutaneous BCCs in order to determine, whether there is difference in the expression pattern related to the histologic subtypes and tumor growth characteristics.

MATERIAL AND METHODS

The study group consisted of 38 BCCs cathegorized into low-risk (non-infiltrative) subroup (8 superficial and 12 nodular subtypes) and high-risk (infiltrative) subgroup (10 nodular-infiltrative and 8 infiltrative subtypes). Specific monoclonal antibody against p120(ctn) was used for staining.

RESULTS

Overall, there were 12 cases (31.6%) with normal preserved and 26 cases (68.4%) with abnormal p120(ctn) expression. In superficial, nodular, nodular-infiltrative and infiltrative subtypes, abnormal p120(ctn) immunoreactivity was found in 37.5% (3/8), 41.7% (5/12), 100% (10/10) and 100% (8/8), respectively. We have confirmed a strong correlation between the expression of p120(ctn) and both given, non-infiltrative and infiltrative BCC growth phenotypes. In the latter subgroup, almost all lesions showed diffusely reduced membranous staining, of which five also manifested an aberrant immunoreactivity in the cytoplasm. This cytoplasmic positivity occurred solely at the invasive front of the infiltrative tumor formations.

CONCLUSION

Our results showed that decreased membranous expression of p120(ctn) was a frequent event in human cutaneous BCC and it was associated with infiltrative growth phenotype. Considering that nearly half of the BCCs with non-infiltrative growth pattern also exhibited reduced membranous expression, aberrant cytoplasmic immunoreactivity of p120(ctn), which was found exclusively in the high-risk BCC variants, can more reliably reflect and predict biological behaviour and malignant potential.

Correlation between E-cadherin and p120 expression in invasive ductal breast cancer with a lobular component and MRI findings

Invasive breast cancer comprises a spectrum of histological changes with purely lobular cancer on one side and purely ductal cancer on the other, with many mixed lesions in between. In a previous study, we showed that in patients with any percentage lobular component at core needle biopsy, preoperative MRI leads to the detection of clinically relevant additional findings in a substantial percentage of patients, irrespective of the percentage of the lobular component. Detection of a small lobular component may however not be reproducible among pathologists. Loss of membrane expression of E-cadherin or p120 is useful biomarkers of ILC and may therefore support a more objective diagnosis. All patients diagnosed with breast cancer containing a lobular component of any percentage between January 2008 and October 2012 were prospectively offered preoperative MRI. Clinically relevant additional findings on MRI were verified by pathology evaluation. Expression patterns of E-cadherin and p120 were evaluated by immunohistochemistry on the core needle biopsy. MRI was performed in 109 patients. The percentage of lobular component was significantly increased in cases with aberrant E-cadherin or p120 expression (both p = <0.001). However, aberrant expression of E-cadherin and p120 was not related to the probability of detecting relevant additional MRI findings. E-cadherin and p120 did not appear to be useful objective biomarkers for predicting additional relevant findings on MRI in patients with a lobular component in the core needle of their breast cancer.

Pancreatic metastasis from invasive pleomorphic lobular carcinoma of the breast: a rare case report

Background

Invasive pleomorphic lobular carcinoma (PLC) is an aggressive subtype of invasive lobular carcinoma of the breast, which has its own histopathological and biological features. The metastatic patterns for PLC are distinct from those of invasive ductal carcinoma. In addition, pancreatic metastasis from PLC is extremely rare.

Case presentation

We report a rare case of a 48-year-old woman presenting with clinical gastrointestinal symptoms and pancreatic metastasis of PLC. The pancreatic tumor was composed of pleomorphic tumor cells arranged in the form of solid sheets and nests and as single files, with frequent mitotic figures, nucleolar prominence, high nuclear to cytoplasmic ratio and loss of cohesion. The malignant cells were positive for p120 (cytoplasmic) and GATA3 and negative for estrogen receptor, progesterone receptor, human epidermal growth factor receptor 2, E-cadherin, gross cystic disease fluid protein 15 and mammaglobin, which indicated a lobular carcinoma phenotype of the breast.

Conclusions

To the best of our knowledge, this is one of the few reported cases in the literature of pancreatic metastasis of invasive lobular carcinoma of the breast, of which the definitive diagnosis was obtained only after surgery. Rare metastasis sites should be considered, particularly, when a patient has a medical history of PLC.

Update on Immunohistochemical Analysis in Breast Lesions

CONTEXT

- The utility of immunohistochemistry (IHC) in breast lesions needs to be updated with exceptions among these lesions. Biomarker studies with IHC in triple-negative breast carcinoma may help develop targeted therapies for this aggressive breast cancer. The distinction of metastatic lung adenocarcinoma to the breast and invasive breast carcinoma has significant prognostic and therapeutic implications. The determination can be challenging because both primary tumors can express estrogen receptor and/or HER2 by IHC, creating a diagnostic dilemma.

OBJECTIVES

- To provide a practical update on the use of IHC markers in differential diagnoses in breast lesions, including benign, atypical, precancerous, and malignant tumors; to highlight recently published research findings on novel IHC markers in triple-negative breast carcinoma cases; and to reinforce the importance of IHC use as an ancillary tool in distinguishing metastatic lung adenocarcinoma to the breast from primary breast carcinoma using real case examples.

DATA SOURCES

- PubMed (US National Library of Medicine, Bethesda, Maryland) literature review and authors' research data and personal experiences were used in this review.

CONCLUSIONS

- Immunohistochemistry has an important role in making differential diagnoses in breast lesions in morphologically equivocal settings; recognizing IHC expression status in the exceptions among these lesions will aid in the correct diagnosis of challenging breast cases. Studies suggest that androgen receptor, p16, p53, GATA3, and PELP1 may have potential diagnostic, prognostic, and predictive value in triple-negative breast carcinoma cases; these findings may provide insight and a greater understanding of the tumor biology in triple-negative breast carcinomas. In distinguishing metastatic estrogen receptor-positive or HER2⁺ lung adenocarcinoma to the breast from primary breast carcinoma, napsin A, TTF-1, and GATA3 comprise a useful IHC panel.