Acinic Cell Carcinoma of the Breast: A Rare and Diagnostically Challenging Entity

Abstract

Acinic Cell Carcinoma (AcCC) of the breast is a rare subtype of invasive breast carcinoma that falls under the category of salivary gland-type tumours of the breast. Histologically, it closely resembles AcCC of the salivary gland. Here, the authors report a case of AcCC of the breast in a 51-year-old woman who presented with a palpable lump in her right breast. Radiological investigation revealed a Breast Imaging Reporting and Data System (BIRADS) score V lesion. A core biopsy was performed, and the histopathological examination revealed relatively bland cells arranged in an acinar pattern within a myxoid stroma, closely resembling adenosis rather than a neoplasm. The diagnosis posed a challenge in the core biopsy due to its close resemblance to adenosis. However, the clinical and radiological findings strongly suggested malignancy. Immunostaining with p63 was conducted, which helped demonstrate the absence of myoepithelial cells around the tumour cell nests and supported the neoplastic nature of the lesion. Despite the bland and low-grade morphology, the tumour was found to be triple negative for Oestrogen Receptor (ER), Progesterone Receptor (PR), and Human Epidermal Growth Factor Receptor 2 (HER2), and it exhibited characteristic positivity for SRY-Box Transcription Factor 10 (SOX 10), S100, and CK7, which aided in making the diagnosis. The authors presented the case report to highlight the rarity of this subtype of breast carcinoma and to emphasise the importance of histomorphology and immunoprofile in reaching a diagnosis. To the best of the authors’ knowledge, the present case was the second reported case of AcCC of the breast from India, adding to the novelty of this case.