So-called acinic cell carcinoma of the breast arises from microgladular adenosis and is not a distinct entity

Breast Carcinomas Resembling Acinic Cell Carcinoma: Comprehensive Analysis of 14 Cases and Review of the Literature

Acinic cell carcinoma (AciCC) of the breast is an exceptionally rare subtype of invasive breast carcinoma, often exhibiting a triple-negative phenotype and relatively indolent behavior. Since the first case reported by Roncaroli and colleagues in 1996, no more than 60 additional cases have been described in English medical journals, usually as case reports or small case series. In this study, we presented an in-depth analysis of 14 cases of AciCC of the breast, including 4 pure AciCCs and 10 AciCCs mixed with other histologic types. We reported the clinicopathologic characteristics, histologic components, treatment modalities including response to neoadjuvant treatment in 3 patients, and outcomes. In addition, we assessed the expression of nuclear transcription factor nuclear receptor subfamily 4 group A member 3 by immunohistochemistry and gene rearrangements by fluorescence in situ hybridization, which has been implicated in AciCC of the salivary gland. All 14 cases were negative for nuclear receptor subfamily 4 group A member 3 expression, and no gene rearrangements were detected. We also conducted a thorough review of the literature to highlight advancements in understanding this rare breast cancer subtype. This study aims to enhance clinical knowledge of AciCC of the breast and contributed to growing evidence that AciCC of the breast and AciCC of the salivary glands appear to be unrelated entities, despite sharing a similar histologic appearance.

Carcinoma arising in microglandular adenosis of the breast: clinicopathological and genetic analysis

AIMS

To study the clinicopathological, immunohistochemical and molecular features of carcinoma arising in microglandular adenosis (MGACA) of the breast.

METHODS

Clinicopathological features of 13 cases of MGACA were analysed. All tumours were molecular subtype by immunohistochemistry (IHC) of AR, CD8, FOXC1 and DCLK1 expression. Next-generation sequencing including 511 genes was analysed.

RESULTS

All tumours showed a histological spectrum ranging from microglandular adenosis (MGA) to atypical MGA (AMGA), ductal carcinoma in situ (DCIS) and MGACA. Invasive components in 10 of 13 tumours were invasive carcinoma of no special type (NST), 3 were metaplastic carcinoma with mesenchymal differentiation (including two cases of matrix-producing carcinoma) mixed with NST. All lesion-associated epithelial cells were triple negative (TNBC) and positive for S-100. Reticulin staining showed the presence of basement membrane in MGA, AMGA and DCIS, and its absence in invasive carcinoma. According to IHC-based TNBC molecular subtyping, 10 tumours were basal-like immune-suppressed (BLIS), 2 were luminal androgen receptor and 1 was immunomodulatory. 10 patients had gene mutations. Pathogenic germline mutations of the BRCA1 and BRCA2 genes were detected in four tumours (30.7%) and one tumour (7.7%). Somatic mutation rate of the TP53 gene was 69.2%. Amplification rates of MYC, FGFR2, JAK2 and MCL1 genes in our cohort were 46.2%, 15.4%, 15.4% and 7.7%, respectively.

CONCLUSION

MGACA is a rare breast carcinoma, with distinct morphological, immunohistochemical and molecular features. Most MGACA were BLIS molecular subtype of TNBC. TP53 and BRCA1 gene mutation and MYC gene amplification were the most common genetic changes in MGACA.

Breast acinic cell carcinoma with weak progesterone receptor expression: a case report and literature review

Rationale

Acinic cell carcinoma (AcCC) of the breast is an extremely rare malignant epithelial tumor characterized by acini cell differentiation, clinical low-grade malignancy, and a molecular triple-negative subtype.

Patient concern

A 47-year-old female presented with a 1-month history of a painless mass in her right breast.

Diagnosis

Ultrasound imaging, mammography and magnetic resonance imaging revealed a lesion, approximately 3.0cm×1.5cm in size, in the right breast, which was considered to be a malignancy. After the surgery, the AcCC of the breast was confirmed histologically.

Interventions

Right breast mastectomy and sentinel lymph node biopsy were performed. Adjuvant chemotherapy included 4 cycles of doxorubicin hydrochloride (Adriamycin) and cyclophosphamide followed by 4 cycles of docetaxel (Taxotere).

Outcomes

The patient was discharged from the hospital after surgery. There was no sign of recurrence during a 9-month follow-up period.

Lessons

Acinic cell carcinoma (AcCC) of the breast is an extremely rare malignant epithelial tumor that can be accurately diagnosed based on histopathologic morphology and immunohistochemistry. The weak positive progesterone receptor (PR) expressed in this case is extremely rare, which may provide a new research direction for the endocrine therapy of AcCC. Both AcCC and microglandular adenosis(MGA) exhibit microglandular growth, and the relationship between them remains unclear. Differentiation between them not only relies on histomorphology and pathological immunohistochemistry but also depends on clinical manifestations and other presentations. Optimal treatment of AcCC is the same as that for invasive breast cancer. The prognosis is generally good, with adjuvant therapy after surgery.

Salivary gland-like tumors of the breast: Histopathologic and genetic features with clinical implications

Salivary gland-like tumors of the breast are rare neoplasms that share morphologic, immunophenotypic, and/or genetic features with their salivary gland counterparts, highlighting a shared underlying histopathogenesis in most cases. Salivary gland-like carcinomas included in the World Health Organization classification of breast tumors are adenoid cystic carcinoma, secretory carcinoma, mucoepidermoid carcinoma, acinic cell carcinoma, and the exceedingly rare polymorphous adenocarcinoma. These carcinomas are usually triple negative for estrogen receptor and progesterone receptor expression and HER2 overexpression, yet generally have favorable prognosis, in contrast to high-grade triple negative carcinomas of no special type. On the other hand, a small subset, such as solid-basaloid adenoid cystic carcinoma, rare high-grade carcinomas, and those associated with transformation to other types of high-grade invasive carcinoma can behave more aggressively. Other salivary gland-like tumors of the breast, such as pleomorphic adenoma and adenomyoepithelioma, are usually benign but can rarely undergo malignant transformation. Although clinical experience with salivary gland-like breast tumors is overall limited, their recognition and accurate classification has important implications for prognosis and clinical management, especially to avoid overtreatment of salivary gland-like carcinomas. The identification of characteristic genetic alterations and/or immunohistochemical surrogates in many of these tumors has practical applications to establishing an accurate diagnosis and directing clinical management. This review highlights the histopathologic and genetic characteristics of salivary gland-like breast tumors and the implications of the diagnosis for current clinical management.

Elucidating the nature of acinic cell carcinoma of the breast with high-grade morphology: evidence from case report

BACKGROUND

Acinic cell carcinoma (AciCC) of the breast is a rare subtype of breast cancer. It was considered a low-grade triple-negative breast cancer (TNBC) with the potential to progress or transform into a high-grade lesion because of the molecular similarities with conventional aggressive TNBC in several genetic studies. Microscopically, the coexistence of classical low-grade and high-grade triple-negative components in breast AciCC is not uncommon. However, there is a scarcity of research on the comparative histopathological and genetic aspects of both components.

CASE PRESENTATION

A 34-year-old woman with a nontender mass in the upper outer quadrant of the left breast was initially diagnosed with a malignant small round cell tumor (undifferentiated or poorly differentiated carcinoma) based on a preoperative biopsy, which was later identified as breast AciCC with a high-grade solid component. Left breast-conserving surgery with sentinel lymph node biopsy was performed. Microscopically, the breast AciCC consisted of a classical acinic component and a high-grade component. The latter demonstrated a solid sheet-like pattern characterized by large, round, pleomorphic or vesicular nuclei, prominent nucleoli, and frequent mitotic activities. Classical acinic architectures focally merged together to form solid nests and transited into high-grade areas. Remarkably, in the high-grade lesion, conventional immunochemical markers for breast AciCC, such as α1-antitrypsin (AAT), Lysozyme (LYS), Epithelial membrane antigen (EMA), S100 protein (S100), and cytokeratin (CK) were negative, whereas cell cycle protein D1 (cyclin D1) and vimentin showed diffuse expression. Next‑generation sequencing (NGS) revealed that 43.5% of variants were identical in both components. Furthermore, PAK5 mutation; copy number (CN) loss of CDH1, CHEK1, and MLH1; and CN gains of CDK6, HGF, and FOXP1 were identified in the high-grade lesion. The patient was treated with eight cycles of adjuvant chemotherapy (epirubicin combined with cyclophosphamide) and radiotherapy after surgery, and she is currently alive for 43 months with no metastases or recurrences.

CONCLUSIONS

This case demonstrates a comparative analysis of the histopathological and genetic characteristics of classical low-grade and high-grade components of AciCC within the same breast. This information may serve as a morphological and molecular basis for further investigation into the molecular mechanisms underlying high-grade lesions in breast AciCC.

Salivary Gland-like Tumors of the Breast

CONTEXT

The World Health Organization classification of tumors of the breast recognizes several special type carcinomas and benign lesions with features comparable to those of salivary gland tumors.

OBJECTIVE

To discuss the histologic, immunophenotypic, molecular, and clinical features of salivary gland-like carcinomas of the breast. These breast tumors are often negative for hormone receptors and human epidermal growth factor receptor 2 (HER2), that is, triple-negative, but they generally have a much better prognosis than triple-negative breast carcinomas of no special type. We compare the immunophenotypic, molecular, and clinical features of these breast tumors with their salivary gland counterparts, highlighting similarities and differences. We also discuss benign salivary gland-like breast tumors. Finally, we highlight recent developments in understanding the molecular pathogenesis of these breast tumors and novel ancillary studies that can be used to support their diagnosis.

DATA SOURCES

A literature review was conducted, and papers were selected for further analysis and discussion by the authors of this review based on their novelty, applicability, and impact in the field.

CONCLUSIONS

Breast tumors that exhibit morphologic overlap with salivary gland tumors have been recognized by pathologists for decades, but the similarities and differences in their molecular pathogenesis have not been understood until more recently. These developments have led to novel diagnostic tools and further knowledge of these rare breast lesions.

NR4A3 Expression Is Consistently Absent in Acinic Cell Carcinomas of the Breast: A Potential Nosologic Shift

Acinic cell carcinoma (AciCC) is a tumor that is recognized in both the breast and salivary glands. Recently, the recurrent genomic rearrangement, t(4;9)(q13;q31) was identified in salivary AciCC that results in constitutive upregulation of the nuclear transcription factor NR4A3, which can be detected by immunohistochemistry. In this study, we sought to evaluate NR4A3 expression in breast AciCC using immunohistochemistry. Strong and diffuse nuclear staining was considered a positive result. Sixteen AciCCs were studied, including 8 pure AciCCs and 8 AciCCs admixed with other types (invasive carcinoma of no special type in 5 cases and metaplastic carcinoma in 3 cases). All 16 AciCCs showed negative results for NR4A3 expression. Four cases with available material were evaluated for rearrangements of the NR4A3 gene by fluorescence in situ hybridization and no rearrangements were observed. Whole-genome sequencing of 1 AciCC revealed a TP53 splice-site mutation, high levels of genomic instability, and genomic features of homologous recombination DNA repair defects; a structural variant analysis of this case did not reveal the presence of a t(4;9) rearrangement. We conclude that breast AciCCs consistently lack NR4A3 rearrangement or overexpression, unlike most of the salivary AciCCs, and that consistent with previous results, breast AciCCs are associated with genomic alterations more similar to those seen in triple-negative breast carcinomas than salivary gland AciCCs. These results suggest that unlike other salivary gland-like tumors that occur in the breast, the molecular underpinnings of the salivary gland and breast AciCCs are different and that the salivary gland and breast AciCCs likely represent distinct entities.

Acinic cell carcinoma of the breast: A comprehensive review

Acinic cell carcinoma of the breast is a rare special subtype of breast cancer in the category of salivary gland-type tumors. It is morphologically similar to acinic cell carcinomas of salivary glands and pancreas and has a triple-negative phenotype (estrogen receptor-negative, progesterone receptor-negative, and Her-2/neu negative). Its molecular genomic features are more similar to triple-negative breast cancer of no special type than to its salivary gland counterpart. However, the clinical course of the mammary acinic cell carcinoma appears to be less aggressive than the usual triple-negative breast carcinomas. This review comprehensively summarizes the current literature on the clinicopathologic, immunohistochemical, and molecular features of this rare and distinct subtype of breast cancer.

Two cases of mammary acinic cell carcinomas with microglandular structures mimicking microglandular adenosis

Acinic cell carcinoma (AcCC) of breast is a rare subtype of triple-negative breast carcinoma demonstrating a wide morphologic spectrum. In this study, we perform a detailed morphologic and immunohistochemical description of two cases of the rare entity and review the published relative literature. Histologically, the two cases both showed predominantly microglandular and solid structures overlapping with the histological features of microglandular adenosis (MGA), and one case presented spindle cell metaplastic carcinoma with chondromyxoid matrix as a minor morphologic pattern. In two cases, most of the cancer cells were positive for lysozyme and antitrypsin strongly and extensively, but negative for estrogen receptor (ER), progesterone receptor (PR), androgen receptors (AR) and human epidermal growth factor receptor 2 (HER2). The true relationship between breast AcCC and MGA or carcinoma arising in MGA(CAMGA) may remain unclear; re-excision is advised when the MGA-like content extends to the surgical margins in the setting of breast AcCC. More cases and further molecular investigations are required to elucidate the true histogenesis and give the patients appropriate treatment.

Low-grade triple-negative breast carcinomas. A report of 2 cases and an update of current concepts

Triple negative breast cancer is defined by the lack of expression of estrogen, progesterone and HER2 receptors. Significant molecular, morphological and clinical heterogeneity is present in this group of neoplasms. Although the majority are high-grade tumors, low-grade triple negative breast cancers can occur and their evolution, molecular characteristics and therapeutic management vary from the former. In the current review, we focus on the histological and immunohistochemical phenotypes of two new low-grade cases: an acinic cell carcinoma and an adenoid cystic carcinoma. Data originated from the pathology department of a third-level hospital over an 18-month period, within a breast cancer screening program. Low-grade triple negative cancers should be suspected in triple negative breast cancers with low proliferative rates as, unlike high-grade tumors, they require a multidisciplinary approach. They can be diagnosed at an early stage by immunohistochemistry using core needle biopsy.

Whole-exome sequencing and RNA sequencing analyses of acinic cell carcinomas of the breast

AIMS

Acinic cell carcinoma (ACC) of the breast is a rare histological form of triple-negative breast cancer (TNBC). Despite its unique histology, targeted sequencing analysis has failed to identify recurrent genetic alterations other than those found in common forms of TNBC. Here we subjected three breast ACCs to whole-exome and RNA sequencing to determine whether they would harbour a pathognomonic genetic alteration.

METHODS AND RESULTS

DNA and RNA samples from three breast ACCs were subjected to whole-exome sequencing and RNA-sequencing, respectively. Somatic mutations, copy number alterations, mutational signatures and fusion genes were determined with state-of-the-art bioinformatics methods. Our analyses revealed TP53 hotspot mutations associated with loss of heterozygosity of the wild-type allele in two cases. Mutations affecting homologous recombination DNA repair-related genes were found in two cases, and an MLH1 pathogenic germline variant was found in one case. In addition, copy number analysis revealed the presence of a somatic BRCA1 homozygous deletion and focal amplification of 12q14.3-12q21.1, encompassing MDM2, HMGA2, FRS2, and PTPRB. No oncogenic in-frame fusion transcript was identified in the three breast ACCs analysed.

CONCLUSIONS

No pathognomonic genetic alterations were detected in the breast ACCs analysed. These tumours have somatic genetic alterations similar to those of common forms of TNBC, and may show homologous recombination deficiency or microsatellite instability. These findings provide further insights into why breast ACCs, which are usually clinically indolent, may evolve into or in parallel with high-grade TNBC.