Background: Neuroendocrine breast carcinomas (NEC) are rare. Carcinomas with mixed composition often behave differently from 'pure' histological types, and the prognosis is determined by the proportion of the more aggressive tumour. The molecular classification helps in making therapeutic decisions.
Case report: A 56-year-old Caucasian woman with palpable and preoperatively biopsied breast tumour was treated with breast-conserving surgery. The histological specimen revealed a 17-mm invasive carcinoma with an equal proportion of neuroendocrine and invasive-ductal differentiation, accompanied by peritumoural ductal carcinoma in situ. TNM classification was pT1c(is), pN0 (0/1sn), G3, L0, V0, Pn0, R0. The diagnosis was enhanced by immunohistochemistry: high positivity for synaptophysin, neuron-specific enolase (NSE), neural cell adhesion molecule (CD56), Ki-67 (proliferation index 46%), estrogen receptor (ER) and progesterone receptor (PR), negative for Her-2-neu and cytokeratin 5/6, resulting in diagnosis of the molecular 'luminal B' subtype. Radiation and adjuvant chemotherapy with six cycles of 5-fluorouracil, epirubicin and cyclophosphamide, followed by tamoxifen and subsequent exemestane for five years, were recommended.
Conclusion: Immunohistochemistry plays a crucial role in the diagnosis of rare cancer subtypes. NEC is characterized by high biological aggressiveness. Molecular classification facilitates therapeutic decisions.