Triple-negative breast carcinomas of low malignant potential: review on diagnostic criteria and differential diagnoses

Targeting malignant adenomyoepithelioma of the breast: clinical insights on multimodal therapy and disease-free survival

Adenomyoepithelioma of the breast (AME) is a rare, biphasic tumor characterized by the coexistence of both epithelial and myoepithelial cell components, which can present as benign, atypical, or malignant forms. We present a 50-year-old female diagnosed with malignant AME (M-AME) exhibiting low-positive estrogen receptor (ER) expression of 5%, alongside pathogenic HRAS Q61R and PIK3CA H1047R mutations. Immunohistochemistry showed low-positive ER, negative progesterone receptor (PR), HER2, and a high Ki-67 index. Sanger sequencing identified HRAS and PIK3CA mutations. The tumor was staged as pT2N0M0 with no lymph node involvement. The patient underwent partial mastectomy, followed by sentinel lymph node biopsy, which showed no metastasis. Postoperatively, she received four cycles of adjuvant chemotherapy, followed by radiotherapy. The patient achieved disease-free survival at 10 months with no recurrence on imaging. This case highlights the challenges of ER classification in M-AME and highlights the significance of molecular profiling in guiding treatment. The concurrent HRAS and PIK3CA mutations suggest potential targeted therapies, emphasizing the importance of a multidisciplinary approach. Further research is needed to establish standardized treatment guidelines for M-AME.

RNA In Situ Hybridization Detection of CRTC1/3::MAML2 Fusions and LINC00473 in Mucoepidermoid Carcinomas and Hidradenomas of Breast, Salivary Glands, and Skin

Genomic rearrangements involving MAML2 have been reported in mucoepidermoid carcinoma (MEC) arising in various anatomical sites, as well as the benign counterpart of hidradenoma (HA). Depending on the location, MAML2-rearranged neoplasms may share morphologic overlap with additional diagnostic entities, including other salivary gland malignancies and cutaneous mimics. In some cases, detection of a CRTC1::MAML2 or less common CRTC3::MAML2 rearrangement by fluorescence in situ hybridization (ISH) or next-generation sequencing may be necessary to help confirm the diagnosis. However, such testing can be time consuming, relatively expensive, and unavailable in many pathology laboratories. We describe the development and validation of an ISH custom BaseScope assay targeting the recurrent breakpoints of CRTC1::MAML2 and CRTC3::MAML2 rearrangements. Moreover, we investigated the diagnostic utility of LINC00473 RNAscope as a surrogate marker for MAML2 fusion status. LINC00473 is a long noncoding RNA reportedly downstream of the CRTC1::MAML2 oncoprotein. We evaluated 227 patient cases, including 30 salivary gland and 2 breast MEC, 14 cutaneous and 8 breast HA, and 173 cases representing >20 potential histologic entities in the differential diagnosis for the presence of each fusion transcript by BaseScope, and a subset of cases (n = 205) for the detection of LINC00473 by RNAscope. RNA ISH was directly visualized by chromogenic signal, and the MAML2 fusion partner could be positively identified in the majority of cases. Overall, RNA ISH demonstrates high concordance with orthogonal testing, with CRTC1/3::MAML2 BaseScope showing 93% sensitivity and 100% specificity and LINC00473 RNAscope showing 92% sensitivity and 99% specificity. RNA ISH for CRTC1/3::MAML2 rearrangements and LINC00473 represent reasonable timely and cost-effective alternatives to fluorescence ISH and next-generation sequencing. Such markers may provide the means for accurate diagnosis to ensure appropriate therapy of MEC and HA-neoplasms that can arise in multiple anatomical sites and be encountered by a wide range of pathologists.

Tall cell carcinoma with reverse polarity of the breast in a young patient: A case report

INTRODUCTION AND IMPORTANCE

Tall cell carcinoma with reverse polarity (TCCRP) is a rare and newly recognized subtype of invasive breast carcinoma, first described in 2003. It shares histological similarities with tall cell papillary thyroid carcinoma, characterized by papillary structures with reverse cellular polarity. Due to its rarity, TCCRP has been poorly understood, and fewer than 100 cases have been reported globally. This report presents the first case of TCCRP in South Tunisia, contributing to the growing body of knowledge regarding this rare tumor.

CASE PRESENTATION

A 34-year-old woman with no significant personal or family history of breast cancer presented with an incidental finding of a 1 cm breast mass. Imaging studies revealed an atypical mass classified as ACR 4a. Histological analysis following lumpectomy showed circumscribed nests of epithelial cells with delicate fibrovascular cores, resembling papillary structures. Immunohistochemical staining revealed diffuse positivity for cytokeratin 5/6 and calretinin, and negativity for estrogen, progesterone, HER-2, and TTF1. The diagnosis of TCCRP was confirmed. The tumor was classified as SBR grade I, with no lymphovascular invasion or carcinoma in situ. No metastasis was observed in the 31 axillary lymph nodes.

CLINICAL DISCUSSION

TCCRP primarily affects women over 60, with a low incidence in younger individuals. It typically presents as a small, palpable breast mass. Histologically, TCCRP exhibits a solid-papillary architecture with tall cells, reverse polarity, and rare foamy histiocytes. Immunohistochemical findings include negative estrogen, progesterone, HER-2, and TTF1 markers, along with positive staining for calretinin. Molecular studies have revealed IDH2 and PIK3CA mutations in the majority of cases. Despite being triple-negative, TCCRP has a favorable prognosis, with low rates of metastasis or recurrence.

CONCLUSION

TCCRP is a rare subtype of invasive breast carcinoma with distinct histological and immunohistochemical features. It is characterized by an indolent clinical course and an excellent prognosis. Conservative surgical management with clear margins is the optimal treatment approach, with no clear indications for lymph node dissection, chemotherapy, or radiotherapy.

Breast cancer histopathology, classification and clinical management: Current perspectives

Breast cancer (BC) manifests as a diverse group of malignancies and presents as a wide array of tumors with distinct morphological, biological and clinical characteristics. Molecular classification of BC serves as the basis for current precision-oriented therapeutic strategies. Upcoming therapeutic strategies will emphasize personalized medicine and tailoring treatments according to each patient's specific needs. These approaches will involve modulating the therapy intensity based on the biological characteristics of tumours and early predictive indicators, allowing for more precise and adaptable care in oncology. Additionally, there remains an unfulfilled requirement for the creation of new medications to treat breast cancer in its early stages, as well as in advanced cases. This review article presents an extensive examination of breast cancer, delving into its prevalence, contributing factors, molecular and cellular features and therapeutic interventions.

Prognostic impact of histological subtyping in triple-negative breast cancer

The impact of special histological types (ST) in triple-negative breast cancer (TNBC) and its association with overall outcome has gained increasing relevance as survival has been linked to specific histological TNBC subtypes. We evaluated the clinicopathological and survival data of 598 patients with 613 TNBCs, including 464 TNBCs of no special type (NST) and 149 TNBCs ST (low-grade, n = 12, 8.1%; high-grade, n = 112, 75.2%; apocrine and androgen receptor-positive [APO AR], n = 25, 16.8%). Patients with low-grade TNBC ST and TNBC ST APO AR were significantly older (P < 0.001) and had a lower Ki67 index (P < 0.001) than those with TNBC NST. Patients with high-grade TNBC ST were significantly older (P = 0.006) and had poorer pathological responses to neoadjuvant chemotherapy (NAC) (P < 0.001) than those with TNBC NST. Significant survival differences were observed between low-grade TNBC ST, TNBC ST APO AR, high-grade TNBC ST, and TNBC NST in the entire study group (DFS, P = 0.002; DDFS, P = 0.001) and in the non-NAC subgroup (OS, P = 0.034; DFS, P = 0.001; DDFS, P < 0.001). Patients with low-grade TNBC ST had the best survival outcomes. Patients with high-grade TNBC ST showed significantly worse outcomes than those with TNBC NST (entire study group: OS, P = 0.049; DFS, P < 0.001; DDFS, P = 0.001; non-NAC subgroup: OS, P = 0.014; DFS, P < 0.001; DDFS, P < 0.001). We conclude that prognostic stratification of TNBC ST is ultimately important for optimizing the therapeutic management of patients with these rare tumor entities.

Dissecting tumor microenvironment from spatially resolved transcriptomics data by heterogeneous graph learning

Spatially resolved transcriptomics (SRT) has enabled precise dissection of tumor-microenvironment (TME) by analyzing its intracellular molecular networks and intercellular cell-cell communication (CCC). However, lacking computational exploration of complicated relations between cells, genes, and histological regions, severely limits the ability to interpret the complex structure of TME. Here, we introduce stKeep, a heterogeneous graph (HG) learning method that integrates multimodality and gene-gene interactions, in unraveling TME from SRT data. stKeep leverages HG to learn both cell-modules and gene-modules by incorporating features of diverse nodes including genes, cells, and histological regions, allows for identifying finer cell-states within TME and cell-state-specific gene-gene relations, respectively. Furthermore, stKeep employs HG to infer CCC for each cell, while ensuring that learned CCC patterns are comparable across different cell-states through contrastive learning. In various cancer samples, stKeep outperforms other tools in dissecting TME such as detecting bi-potent basal populations, neoplastic myoepithelial cells, and metastatic cells distributed within the tumor or leading-edge regions. Notably, stKeep identifies key transcription factors, ligands, and receptors relevant to disease progression, which are further validated by the functional and survival analysis of independent clinical data, thereby highlighting its clinical prognostic and immunotherapy applications.

Clinicopathological, immunohistochemical and molecular features of acinic cell carcinoma of the breast

Breast acinic cell carcinoma (ACC) is a rare subtype of breast cancer. Accurate diagnosis of ACC using core needle biopsy (CNB) is pivotal for the use of effective treatments and patient prognosis. In the present study, a detailed analysis of the morphological, immunohistochemical and gene mutation features of 2 cases of ACC was performed. CNB was performed prior to surgical excision. The breast ACC in the present cases exhibited overt burrowing labyrinthine networks or 'hand-holding-hand' features. The tumor cells in both of the present cases expressed cytokeratin (CK)7, S100 and CK5/6, but were negative for p63, estrogen receptor and progesterone receptor. GATA binding protein 3 was positive in case 1 but negative in case 2. Fluorescence in situ hybridization indicated no ETS variant transcription factor 6 break-apart probe detection. Next-generation sequencing results revealed the same mutation and a similar abundance in exon 27 (NM_005120.2; c.3817G>T; p.A1273S) of the mediator of RNA polymerase II transcription, subunit 12 homolog (MED12) gene in both patients. To conclude, the findings of the present study suggested that recognition of this rare 'hand-holding-hand' structure could potentially be beneficial for avoiding patient misdiagnosis. In addition, it could be suggested that a mutation in the MED12 exon 27 was associated with the formation of a burrowing labyrinthine network or 'hand-holding-hand' feature.

Molecular pathology in breast disease: diagnostic, prognostic, and therapeutic tools

Molecular testing in breast cancer gained increasing attention and importance as specific molecular results can tailor not only oncological decisions on systemic adjuvant or neoadjuvant or in metastatic setting, but increasingly serve in diagnostic routine histopathological services to differentiate between morphologically overlapping or ambiguous histological pictures. Diagnostic tools involve in most cases a broad spectrum of immunohistochemical panels, followed by entity-specific in situ hybridization probes and in given cases NGS-based sequencing. Workflow of which methodology is applied and in which order depends on the specific entity resp. on the given differential diagnosis in question. Regarding prognostic/predictive molecular testing, the choice of assay and the workflow are based on clinical algorithms and on the evidence of targeted therapies following the molecular alterations. In this review paper, we aim to address the use of molecular technics in [1] the histological diagnostic setting (such as subtyping of invasive carcinomas/malignant spindle cell tumors and sarcomas and some B3 lesions) and [2] in the context of adjuvant or neoadjuvant or other clinical settings with special focus of targeted therapies.

Genetic and Immunohistochemical Profiling of Mammary Hidradenoma and Comparison to Mucoepidermoid Carcinoma

Mucoepidermoid carcinoma (MEC) is exceedingly rare in the breast, with <45 cases reported in the literature. Although estrogen receptor/progesterone receptor/human epidermal growth factor 2 triple-negative, MEC is characterized as a special subtype of breast carcinoma with significantly better prognosis than conventional basal-type tumors. Cutaneous hidradenoma (HA) is considered a benign adnexal neoplasm showing histomorphologic overlap with MEC. Rare cases of HA have also been reported in the breast, but these are relatively uncharacterized. In this study, we examined the clinicopathologic, immunohistochemical (IHC), and genetic features of 8 breast HAs, in comparison to 3 mammary MECs. All cases were positive for MAML2 break-apart fluorescence in situ hybridization. Eight cases demonstrated a CRTC1::MAML2 fusion, and one MEC harbored a CRTC3::MAML2 fusion; the latter is a novel finding in the breast. Mutational burden was very low, with only one HA exhibiting a MAP3K1 pathogenic alteration. By IHC, both MEC and HA demonstrated cell type-dependent expression of high- and low-molecular-weight keratins and p63, as well as negative to low-positive estrogen receptor and androgen receptor. Smooth muscle myosin and calponin highlighted an in situ component in the 3 cases of MEC; expression of these myoepithelial markers was negative in HAs. Additional distinguishing characteristics included the growth pattern and tumor architecture, the presence of glandular/luminal cells in HA, and overall higher IHC expression of SOX10, S100 protein, MUC4, and mammaglobin in MEC. Morphologic findings were also compared to a series of 27 cutaneous nonmammary HAs. Mucinous and glandular/luminal cells were identified in significantly more mammary HAs than nonmammary lesions. The findings provide insight into the pathogenesis of MAML2-rearranged neoplasms of the breast, underscore the overlapping genetic features of MEC and HA, and highlight similarities to their extramammary counterparts.

Analysis of the PARP1, ADP-Ribosylation, and TRIP12 Triad With Markers of Patient Outcome in Human Breast Cancer

PARP inhibitors (PARPi) are increasingly used in breast cancer therapy, including high-grade triple-negative breast cancer (TNBC) treatment. Varying treatment responses and PARPi resistance with relapse currently pose limitations to the efficacy of PARPi therapy. The pathobiological reasons why individual patients respond differently to PARPi are poorly understood. In this study, we analyzed expression of PARP1, the main target of PARPi, in normal breast tissue, breast cancer, and its precursor lesions using human breast cancer tissue microarrays covering a total of 824 patients, including more than 100 TNBC cases. In parallel, we analyzed nuclear adenosine diphosphate (ADP)-ribosylation as a marker of PARP1 activity and TRIP12, an antagonist of PARPi-induced PARP1 trapping. Although we found PARP1 expression to be generally increased in invasive breast cancer, PARP1 protein levels and nuclear ADP-ribosylation were lower in higher tumor grade and TNBC samples than non-TNBCs. Cancers with low levels of PARP1 and low levels of nuclear ADP-ribosylation were associated with significantly reduced overall survival. This effect was even more pronounced in cases with high levels of TRIP12. These results indicate that PARP1-dependent DNA repair capacity may be compromised in aggressive breast cancers, potentially fueling enhanced accumulation of mutations. Moreover, the results revealed a subset of breast cancers with low PARP1, low nuclear ADP-ribosylation, and high TRIP12 levels, which may compromise their response to PARPi, suggesting a combination of markers for PARP1 abundance, enzymatic activity, and trapping capabilities might aid patient stratification for PARPi therapy.

Rare subtypes of triple negative breast cancer: Current understanding and future directions

Rare subtypes of triple-negative breast cancers (TNBC) are a heterogenous group of tumors, comprising 5-10% of all TNBCs. Despite accounting for an absolute number of cases in aggregate approaching that of other less common, but well studied solid tumors, rare subtypes of triple-negative disease remain understudied. Low prevalence, diagnostic challenges and overlapping diagnoses have hindered consistent categorization of these breast cancers. Here we review epidemiology, histology and clinical and molecular characteristics of metaplastic, triple-negative lobular, apocrine, adenoid cystic, secretory and high-grade neuroendocrine TNBCs. Medullary pattern invasive ductal carcinoma no special type, which until recently was a considered a distinct subtype, is also discussed. With this background, we review how applying biological principals often applied to study TNBC no special type could improve our understanding of rare TNBCs. These could include the utilization of targeted molecular approaches or disease agnostic tools such as tumor mutational burden or germline mutation-directed treatments. Burgeoning data also suggest that pathologic response to neoadjuvant therapy and circulating tumor DNA have value in understanding rare subtypes of TNBC. Finally, we discuss a framework for advancing disease-specific knowledge in this space. While the conduct of randomized trials in rare TNBC subtypes has been challenging, re-envisioning trial design and technologic tools may offer new opportunities. These include embedding rare TNBC subtypes in umbrella studies of rare tumors, retrospective review of contemporary trials, prospective identification of patients with rare TNBC subtypes entering on clinical trials and querying big data for outcomes of patients with rare breast tumors.

Mucoepidermoid carcinoma of the breast, 3 cases report and literature review

RATIONALE

Mucoepidermoid carcinoma (MEC) is one of the most common malignant tumors in salivary glands, with specific histomorphological and molecular characteristics. MEC occurring in breast is more rare.

PATIENT CONCERNS

We reported 3 cases of female breast mass, diagnosed as benign nodules by ultrasound.

DIAGNOSES

The first 2 cases were pathological diagnosed as breast MEC, low grade, and the third case as breast MEC, medium grade.

INTERVENTIONS

After pathological diagnosis, 3 patients have expanded the scope of breast resection and lymph node dissection, with negative margin and no lymph node metastasis.

OUTCOMES

In the follow-up observation, the first case was followed up for 24 months, the second case was followed up for 30 months, and the third case was followed up for 12 months. All patients had a good prognosis without evidence of recurrence and metastasis.

CONCLUSION

Breast MEC is extremely rare and estrogen receptor, progesterone receptor, and human epidermal growth factor receptor-2 negative breast cancer with a good prognosis, which is different from other highly malignant triple-negative breast cancers. reviewed its clinicopathologic morphological characteristics, immunohistochemical markers and molecular characteristics, prognosis and clinical treatment through literature, in order to understanding its clinicopathology and providing reference for clinical precise treatment.

The molecular landscape of breast mucoepidermoid carcinoma

Mucoepidermoid carcinoma (MEC) of the breast is an extremely rare salivary gland-type tumor characterized by epidermoid, basaloid, intermediate, and/or mucinous cells arranged in solid and cystic patterns. Despite their triple-negative phenotype, breast MECs are generally considered low-risk malignancies but their biology is largely unexplored; therefore, guidelines for clinical management are lacking. Here, we sought to characterize the molecular landscape of breast MECs. Thirteen cases were histologically reviewed, characterized for tumor-infiltrating lymphocytes (TILs), and were subjected to immunohistochemistry for programmed death-ligand 1 (PD-L1, clone 22C3), EGFR, and amphiregulin (AREG). Rearrangements in MAML2 and EWSR1 were investigated by fluorescent in situ hybridization. Targeted next-generation sequencing of 161 genes was performed on eight cases. Most MECs had low histological grade (n = 10, 77%), with the presence of TILs (n = 9/12; 75%) and PD-L1 combined positive score ranging from 10 to 20 (n = 4/6; 67%). All cases showed EGFR and AREG overexpression and were fusion negative. Enrichment of genetic alterations was observed in PI3K/AKT/mTOR and cell cycle regulation pathways, while only one case harbored TP53 mutations. This is the first study providing extensive molecular data on breast MECs and the largest collection of cases available to date in the literature. Breast MECs lack TP53 mutations found in high-grade forms of triple-negative breast cancers and MAML2 or EWSR1 rearrangements pathognomonic of salivary MECs. Triple-negativity and PD-L1 positivity suggest a window of opportunity for immunotherapy in these patients. The EGFR/AREG axis activation, coupled with the mutational patterns in PI3K/AKT/mTOR and cell cycle pathways warrants caution in considering MECs as low-risk neoplasms.

A case of extensively spreading acinic cell carcinoma of the breast with microglandular features

Acinic cell carcinoma (ACC) is an exceptionally rare type of breast carcinoma with a low-grade morphology and a favorable prognosis. It is postulated to be a type of invasive carcinoma arising in microglandular adenosis (MGA). We report a case of extensively spreading ACC of the breast with MGA-like features. Macroscopically, yellowish nodules were widely distributed throughout the right breast, up to the axilla, without mass formation. Microscopically, the tumor consisted of two distinct carcinoma components: one was multiple nodular lesions showing invasive carcinoma with fused solid nests, and the other was a widely spreading lesion exhibiting MGA-like features with uniform small single glands. Immunohistochemically, both components were negative for ER, PR, and HER2, and expressed EMA, S100 and lysozyme. The distinct morphology and molecular expression indicated ACC. The single glands in the MGA-like area lacked myoepithelial cells but were linearly surrounded by type IV collagen, a basement membrane component. This case supports the hypothesis that ACC and MGA have the same lineage and indicates that ACC is not necessarily a low-grade malignancy and can be aggressive.

Breast lesions with myoepithelial phenotype

Myoepithelial cells (MECs) constitute a continuous layer of cells surrounding the breast glands, localised between the epithelial cells (ECs) and the basal membrane. MECs play important roles in normal mammary gland as they produce basal membrane and stimulate secretion. During neoplastic transformation, MECs act as a barrier preventing stromal invasion. MECs themselves can undergo a great variety of changes, ranging from hyperplastic to metaplastic, to neoplastic, and giving rise to a wide spectrum of morphological pictures sometimes difficult to interpret on routine diagnoses. Several benign and malignant breast tumours can present features of MECs differentiation. As these latter tumours are quite infrequent, the purpose of the present study is to offer a review of the morphological spectrum of MECs lesions, with correlations to prognosis.

Low-risk triple-negative breast cancers: Clinico-pathological and molecular features

Triple-negative breast cancers (TNBC) comprise biologically and clinically heterogeneous diseases characterized by the lack of hormone receptors (HR) and HER2 expression. This subset of tumors accounts for 15-20% of all breast cancers and pursues an ominous clinical course. However, there is a spectrum of low-risk TNBCs with no/minimal metastatic potential, including the salivary gland-type tumors, those with extensive apocrine differentiation and/or high tumor-infiltrating lymphocytes, and small-sized, early-stage (pT1a/bN0M0) TNBCs. De-escalating the treatment in low-risk TNBC, however, is not trivial because of the substantial lack of dedicated randomized clinical trials and cancer registries. The development of new diagnostic and/or prognostic biomarkers based on clinical and molecular aspects of low-risk TNBCs would lead to improved clinical treatment. Here, we sought to provide a portrait of the clinicopathological and molecular features of low-risk TNBC, with a focus on the diagnostic challenges along with the most important biological characteristics underpinning their favorable clinical course.