medullary carcinoma of breast
An uncommon type–5% of all breast carcinomas–of infiltrating ductal carcinoma affecting women under age 50, which is more common in the Japanese and in those with the BRCA1 mutation.
Prognosis 84% 10-year survival vs ductal carcinoma, 63%.
Macro Well-circumscribed, soft, rounded and cystic tumour mass with pushing rather than infiltrating margin; it is often large before it metastasizes to axillary lymph nodes; lesions may be haemorrhagic and necrotic
Micro Clusters and sheets of cells with indistinct cell borders, lacking glandular or ductal differentiation, arranged in a syncytial pattern; cells have abundant eosinophilic cytoplasm, large bizarre and pleomorphic or anaplastic nuclei, prominent nucleoli, and frequent mitoses, and a prominent lymphoplasmacytic inflammation peripheral to “pushing” tumour margins, which consists of peripheral T-cells including activated cytotoxic lymphocytes and IgA plasma cells that are a host response to the tumour.
References Modern Pathology (2010) 23, 1357–1363; doi:10.1038/modpathol.2010.123