We report on a breast carcinoma with medullary features diagnosed by core needle biopsy in a 72-year-old woman. Both the primary tumour and its fine needle aspiration-proven, rapidly growing axillary metastasis regressed completely in less than 2 months, by the time surgery was performed. The biopsy of the primary tumour demonstrated a dense stromal infiltrate of CD8+/granzyme B+ activated cytotoxic T-cells suggestive of a robust antitumour immune response. Paradoxically, both tumour cells and tumour infiltrating immune cells demonstrated a diffuse PD-L1 expression, revealing that antitumour immune response has the ability to spontaneously overcome inhibitory mechanisms induced by cancerous growth.
Keywords: spontaneous regression; triple-negative breast cancer; tumour-infiltrating lymphocytes; PD-L1.