Periocular Sebaceous Carcinoma: case audit from the National Specialist Ophthalmic Pathology Service in Liverpool from 2009 to 2022, to assess the diagnostic utility of PRAME expression.

Introduction: Periocular sebaceous carcinoma (PSC) remains a common diagnostic pitfall both clinically and histomorphologically. PRAME (PReferentially Expressed Antigen in MElanoma) has been studied in the various neoplasms as proposed as diagnostic and therapeutic markers. PRAME is expressed in normal sebaceous units and in some sebaceous lesions; however, its utility in sebaceous carcinoma diagnosis has not yet been extensively investigated. We conducted a 13-year retrospective review of the patients diagnosed with PSC at the National Specialist Ophthalmic Pathology Service in Liverpool. Herein, we report the histomorphological and immunohistochemical (IHC) features of these tumors, particularly PRAME expression in this cohort. Methods: Thirty-one PSC cases diagnosed between 2009 to 2022 were retrieved from the histopathology archives. Twenty cases diagnosed as invasive PSC and 11 cases with in-situ PSC were included. The hematoxylin and eosin (H&E) slides and previously-performed IHC slides were reviewed; clinical information data were obtained. Cases with an adequate tissue were also stained for PRAME (PReferentially expressed Antigen in MElanoma) and adipophilin (if not already performed). Results: In total, there were 24 females and 7 males diagnosed with PSC, ranging from 55 to 90 years (median, 78 years). The types of specimens received were: 11 conjunctival mapping biopsies, 19 excisions/wedge resections, and 1 orbital exenteration. The eyelid was the commonest site involved (n=24), followed by eyelid with conjunctiva (3), and conjunctiva alone (4). All patients presented with the clinical suspicion of malignancy. Histologically, 11 invasive PSC (55%) exhibited poorly differentiated morphology, composed of predominantly atypical basaloid cells with minimal sebocytic differentiation; 9 cases (45%) were moderately-differentiated with noticeable finely multivacuolated cytoplasm; and 3 (15%) showed associated comedo-necrosis. Most invasive PSC showed moderate to brisk mitotic activities. Of those cases with available immunostains (n=31), 25 (80.6%) expressed adipophilin; 18 (58.1%) Ber-EP4; 14 (45.2%) epithelial membrane antigen (EMA); and 5 (16.1%) both androgen receptor and perforin positivity. PRAME expression was seen in normal sebaceous glands; however, only (5/19; 26%) of invasive PSC showed focal weak-to-moderate PRAME positivity, and mostly in moderately-differentiated tumors. None of the in-situ PSC were PRAME positive. Conclusions: Most PSC are moderate- to poorly-differentiated. Although PRAME is expressed in normal sebaceous units, it appears less useful as diagnostic marker for PSC, especially in poorly-differentiated tumors. In difficult cases, panels of immunohistochemical studies (Adipophilin, Ber-EP4 and EMA) achieve a definitive diagnosis.