Metaplastic Carcinoma with Chondroid Differentiation Arising in Microglandular Adenosis

New insights into acinic cell carcinoma of the breast: clinicopathology, origin of histology, molecular features, prognosis, and treatment

Acinic cell carcinoma (AciCC) of the breast is a rare malignant epithelial neoplasm, with approximately 60 cases reported in the literature. It predominantly affects women and exhibits significant histological heterogeneity. The diagnosis of breast AciCC is primarily based on the presence of eosinophilic and/or basophilic granular cytoplasm and markers of serous acinar differentiation. Despite being considered a low-grade variant of conventional triple-negative breast cancer (TNBC), over 25% of patients with breast AciCC have adverse clinical outcomes. Additionally, in early research, microglandular adenosis (MGA) and atypical MGA were considered potential precursors for various breast cancers, including intraductal carcinoma, invasive ductal carcinoma, adenoid cystic carcinoma, metaplastic carcinoma, and AciCC. Similarly, some studies have proposed that breast AciCC should be considered a type of carcinoma developing in MGA with acinic cell differentiation rather than a distinct entity. Therefore, the pathogenesis of breast AciCC has not yet been clarified. Moreover, to the best of our knowledge, the literature has not summarized the latest prognosis and treatment of breast AciCC. In this review, we synthesized the current literature and the latest developments, aiming at exploring the clinicopathology, histological origin, molecular features, prognosis, and treatment of breast AciCC from a novel perspective.

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.

Metaplastic Matrix-Producing Carcinoma and Apocrine Lobular Carcinoma In Situ Associated with Microglandular Adenosis: A Unique Case Report

Microglandular adenosis is a non-lobulocentric haphazard proliferation of small round glands composed of a single layer of flat to cuboidal epithelial cells. The glandular structures lack a myoepithelial layer; however, they are surrounded by a basement membrane. Its clinical course is benign, when it is not associated with invasive carcinoma. In around 30% of cases, there is a gradual transition to atypical microglandular adenosis, carcinoma in situ, and invasive breast carcinoma of several different histologic subtypes, including an invasive carcinoma of no special type, metaplastic matrix-producing carcinoma, secretory carcinoma, metaplastic carcinoma with squamous differentiation, acinic cell carcinoma, spindle cell carcinoma, and adenoid cystic carcinoma. Recent molecular studies suggest that microglandular adenosis is a non-obligate precursor of triple-negative breast carcinomas. In this manuscript, we present a unique case of microglandular adenosis associated with metaplastic matrix-producing carcinoma and HER-2 neu oncoprotein positive pleomorphic lobular carcinoma in situ with apocrine differentiation in a 79-year-old patient.

Salivary gland-type mammary carcinoma arising in microglandular adenosis: A case report and clinicopathological review of the literature

INTRODUCTION

Microglandular adenosis (MGA) is a rare benign proliferative lesion lacking a myoepithelial cell layer; 27% of all reported cases have progressed to invasive carcinoma. Salivary gland-type carcinomas of the breast are also uncommon, representing 2% of all breast cancers. This wide spectrum of neoplasms tends to be triple negative and generally has an excellent prognosis. Given the rarity of salivary gland-type carcinomas of the breast arising from MGA, there are few reports of these cases in literature. As such, there is uncertainty regarding their diagnosis and treatment strategies.

PRESENTATION OF CASE

We report the rare case of a 66-year-old woman who presented with a triple negative, invasive carcinoma with salivary gland-type features, arising from MGA. The patient underwent mastectomy with sentinel lymph node biopsy, followed by Taxotere and Cyclophosphamide (TC) chemotherapy and 50 Gy in 25 fractions of radiation to her chest wall. We reviewed the available literature on salivary gland-type breast carcinomas arising from MGA.

DISCUSSION

Despite the generally unfavourable characteristics associated with carcinoma arising in microglandular adenosis (MGACA), most patients with MGACA have favourable outcomes.

CONCLUSIONS

The findings of the present case and reviewed cases are consistent with the literature on MGA, atypical MGA (AMGA), and MGACA. Future study of this rare entity is warranted to establish a consensus surrounding its clinical significance and treatment methods.