Introduction: Several rare metastatic melanoma variants exist with unique clinical, histopathological and immunohistochemical features. Case: We present the case of a 44-year-old lady with BRAF mutant metastatic melanoma who presented with a rapidly growing mass in the left groin while on combination immunotherapy of ipilimumab and nivolumab. Her background was of a primary T4b nodular melanoma (BT 4.8mm), excised from the left mons pubis less than one year earlier, with a positive sentinel lymph node biopsy from the contralateral groin. Following staging, a left groin dissection was performed returning histopathology results consistent with sarcomatoid dedifferentiated metastatic melanoma. Histology revealed the mass was comprised of spindled and sarcomatoid cells. It tested negative for melanoma markers S100, Sox-10 and Melan-A and negative for sarcoma markers. Further molecular testing was strongly positive for BRAF V600E mutation. Discussion: Metastatic sarcomatoid dedifferentiated melanoma is a very rare and highly aggressive subtype of metastatic melanoma defined by a loss of conventional melanoma histological and immunohistochemical features, more closely resembling a sarcoma. It often develops despite patients being on immunotherapy or targeted therapy and presents both a diagnostic and therapeutic dilemma for clinicians. Reference: Lowe, L 2023. ‘Metastatic melanoma and rare melanoma variants: a review’. Pathology 55, issue 2, pp 236-244.