Abstract

The SMARCA subgroup of genes belong to the SWI1/SNF1 family that are responsible chromatin remodelling and repair. Inactivating mutations in the main SMARCA genes A2 and A4 lead to loss of expression of their respective proteins within the nucleus and, as such have characterised a set of malignancies that are underpinned by SMARCA-deficiency.

The morphology of these tumours ranges from small to large epithelioid cells, giant cells and rhabdoid cells. The rhabdoid cells are frequently present in these tumours but are not a sine qua non for the diagnosis. Most of these tumours are undifferentiated or dedifferentiated, high-grade pleomorphic carcinomas. Focally, areas of better differentiation can be seen. The initial description of a SMARCA4-deficient malignancy was the small cell carcinoma of the ovary, hypercalcaemic type. Subsequently, tumours fitting this characteristic morphology and immunophenotype have been described in the lung, thoracic cavity, endometrium and sinonasal tract, gastrointestinal tract and kidney. Immunohistochemical loss of SMARCA2 and SMARCA4 may occur concomitantly or independently of each other.

SMARCA-deficient malignant tumours represent a unique subset of tumours with typical morphological and immunohistochemical findings.