Introduction: The special types of breast cancer seem to have not only distinct morphological features but also distinct biological features.
Materials and methods: Women diagnosed with a first primary invasive breast cancer in the 2004-2005 period were identified through Tuscan Cancer Registry. Information on age, tumor size, lymph node status, histological type and grade, hormonal receptors, HER2 immunohistochemical expression were collected. Five subtypes were defined: luminal A, luminal B HER2+, luminal B HER2-, triple negative, and HER2 positive. The association between the histological type and molecular subgroups was assessed by a Fisher's exact test, and a multinomial logistic regression model was used.
Results: Out of 1,487 patients, 34 % were luminal A subtype, 25 % luminal B HER2-, 11 % luminal B HER2+, 19 % triple negative, and 10.2 % HER2+; 58.5 % of cancers were ductal NOS types. With luminal A as reference, histological types distribution was significantly different between the subgroups. Mucinous, tubular, and cribriform histotypes were found among luminal A cancers more than in other subgroups; all medullary carcinomas were triple negative cancers. Pathological stage at diagnosis was more advanced, and histological grade was lower among subgroups other than luminal A.
Conclusions: Significant association between breast cancer histotypes and molecular subgroups was found.