MRC1 and sebaceous gland neoplasm: MTS is a clinical diagnosis based on the presence of at least one sebaceous gland tumor (benign or malignant) and at least one Lynch syndrome-associated malignancy [2,4]. Additional diagnostics include histopathology consistent with sebaceous differentiation, germline genetic testing for MMR gene mutations, and microsatellite instability testing - the hallmark of MMR gene deficiency.