Be smart about SMARC(A4)

Abstract

SMARCA4-deficient undifferentiated malignant neoplasms SD-UMN comprise a group of aggressive tumours with epithelioid or rhabdoid morphology and loss of function of SMARCA4 a component of the SWItch Sucrose Nonfermentable chromatin remodelling complex SD-UMNs first recognised in the thoracic cavity is now known to occur at multiple anatomic sites 1 We present a case of a 72-year-old man who presented with cutaneous lesions on his scalp ear and lower back While his head and neck lesions showed a squamous cell carcinoma histopathological examination of his back lesion revealed an undifferentiated tumour with sheets of highly pleomorphic cells and high mitotic activity A broad range of immunohistochemical stains were performed but they were non-contributory Subsequent axillary dissection revealed metastatic lymph nodes with a similar morphological and immunohistochemical profile SMARCA4 immunohistochemical stain was then performed on both primary and metastatic lesions which showed complete loss of expression Only three cases of primary cutaneous SD-UMNs have been reported in the literature and none with metastases 2 While it is known that thoracic and visceral SD-UMNs behave aggressively and carry poor prognosis limited information is available about their cutaneous counterparts This case highlights the importance of thorough investigation to rule out cutaneous SD-UMNs in suspected cases