Differential immunohistochemical and biological profile of squamous cell carcinoma of the breast.

ABSTRACT

BACKGROUND: Pure or metaplastic squamous cell carcinoma (SCC) of the breast is a rare entity with an unclear pathogeny and aggressive clinical behaviour. An attempt was made to characterize its differential immunohistochemical and biological profile. PATIENTS AND METHODS: Twenty-seven cases of SCC (pure or not) of the breast were matched with 27 ductal invasive carcinomas (IDC) for age, tumour size, nodal involvement and year of diagnosis. The expression levels of oestrogen receptor (ER), progesterone receptor (PR), Ki-67, epidermal growth factor receptor (EGFR), HER2, Cyclin Bl, hTERT, cytokeratins (CK) 5/6 and p63 were determined immunohistochemically in both cohorts. The presence of the human papilloma virus (HPV) genome was investigated by polymerase chain reaction (PCR). RESULTS: Pure and metaplastic SCC displayed common profiles typifying a basal origin they never expressed ER or PR, were HER2-negative in 93% of cases, exhibited positivity for CK5/6 or EGF-R in 75% and 85%, and for p63 in 70% of cases and were highly proliferative. These profiles were markedly different from those of matched controls (p<0.001 for five markers) except for HER2 and hTERT. The HPVgenome was detected in 2 out of 14 cases (14%) of SCC. CONCLUSION: The expression profile of SCC of the breast was markedly different from that of IDC. A typical "basal-like" phenotype was displayed that may explain part of their behaviour and justify specific therapeutic approaches. HPV infection was not a leading oncogenic event in SCC of the breast.