Case report – mammary adenoid cystic carcinoma, solid type with basaloid features and metaplastic heterologous elements

Adenoid cystic carcinoma is a rare type of invasive breast cancer that is generally considered to have a favourable prognosis. We report a rare case of mammary adenoid cystic carcinoma in a 66-year-old female with solid and basaloid morphology and meta-plastic heterologous elements. The tumour was 10 mm on resection and had predominantly solid architecture and a conspicuous dual cell population on immunohistochemistry. There were areas of benign bone intermixed with the tumour, and review of the core biopsy specimen showed areas of malignant chondroid differentiation. Mammary adenoid cystic carcinoma with solid or basaloid morphology has been reported to have a poorer prognosis than tumours showing other patterns. Reports of this tumour type with divergent differentiation are rare, therefore the clinical significance and prognosis is uncertain.