S-100 Protein-Negative Secretory Breast Carcinoma: Case Report of a Rare Entity

Secretory breast carcinoma represents a rare subtype within basal-like tumours of the breast, having an excellent prognosis, in stark contrast with other basal-like tumours. These tumours are typically ER, PR and HER-2 negative, and S-100 positive. Recurrences are far and few, and treatment is predominantly surgical. We report here a unique case of S-100 marker-negative secretory breast carcinoma in an adult female with a clinical presentation and histo-morphological features otherwise typical of secretory breast carcinomas. This case was managed with radical surgery and adjuvant chemotherapy. Secretory breast carcinomas are unique among basal-like tumours in having an excellent prognosis. They may however be part of a larger spectrum of secretory carcinomas across several glandular organs, with the recently discovered ETV6-NTRK3 fusion gene as a common, recurring mutation. The significance of absence of S-100 staining is not yet clear; however, it may portend a worse prognosis, warranting more aggressive therapy.