PRAME immunostain expression in sebaceous lesions, cutaneous carcinomas and adnexal structures

The use of immunostain for PRAME antigen is well established for cutaneous melanolocytic lesions. However, its staining in other cutaneous structures and lesions is under reported. This study assessed PRAME staining in a large cohort of normal skin tissue, sebaceous lesions, and cutaneous carcinomas to better delineate patterns of PRAME immunoreactivity. PRAME immunostaining was performed on sections of sebaceous lesions and tissue microarrays of basal cell carcinomas (BCCs) and squamous cell carcinomas (SCCs). Normal cutaneous adnexal structures were assessed on the sections of sebaceous lesions. For sebaceous lesions and non-lesional sebaceous glands, PRAME immunostaining was assessed for mature, germinative and sebocytes independently. A total of 193 sebaceous lesions, 64 BCCs and 35 SCCs were stained for PRAME immunostain. Staining pattern was predominantly cytoplasmic in normal apocrine glands, germinative sebocytes of sebaceous glands, and hair germs (p<0.001). Lesional sebocytes did not show different staining compared to normal sebaceous glands (p>0.05). Rare nuclear staining was observed in the normal epidermis (0.6%) and junctional melanocytes (4.1%). BCC, SCC and sebaceous carcinoma all showed low levels of PRAME immunoreactivity with variable proportions of cases demonstrating nuclear staining (BCC 59.4%, SCC 37.1%, sebaceous carcinoma 5.3%). PRAME immunostaining is positive in germinative sebocytes, various cutaneous structures and carcinomas. Nuclear staining, identical to melanoma, was observed in normal epidermis, junctional melanocytes, BCCs, SCCs, and sebaceous carcinomas. The pattern of PRAME staining in the skin must be recognised to avoid pitfalls in interpretating PRAME immunostain.