Squamous cell carcinoma of the breast, are there two entities with distinct prognosis? A series of 39 patients

Purpose: Squamous cell carcinoma (SCC) of the breast is a rare entity of breast cancer, with a very poor prognosis, and whose pathophysiology is still unwell established. Therapeutic management is very heterogeneous due to its incomplete understanding. Nevertheless, it seems that two histological entities can be distinguished: pure SCC close to the cutaneous origin, and metaplastic squamous breast cancer (MSBC). The aim of this study is therefore to assess the difference in survival according to the histological type (SCC or MSBC) and to describe the demographic, clinical, and therapeutic characteristics of the two underlying populations. Methods: Our data came from a monocentric retrospective series of 39 patients treated between 1985 and 2018 at the Gustave Roussy Institute (France) for a breast SCC. Results: Of the 39 patients included, 64% had MSBC and 36% had a pure form. The overall and recurrence-free survival at 3 years [CI 95%] was 72.3% [56.9%; 87.0%] and 67.2% [51.2%; 83.2%], respectively. The overall 3-year survival of patients with MSBC was significantly lower than that with pure SCC: HR [CI 95%] 9.5 [1.2; 73.1], p = 0.008. The 3-year recurrence-free survival of patients with MSBC was also poorer: HR [CI 95%] 11.9 [1.6; 90.7], p = 0.002. Patients with MSBC also tended to be younger, have a large lesion size, and be more metastatic. Conclusion: The histological nature of SCC seems to bring fundamental new elements to the therapeutic management as it impacts recurrence and survival. It should therefore be better characterized at diagnosis in order to possibly adapt treatments.