Conjunctival nevi and melanoma: multiparametric immunohistochemical analysis, including p16, SOX10, HMB45, and Ki-67

The role of p16 in the diagnosis and prognosis of conjunctival melanocytic lesions in the context of other clinical and immunohistochemical parameters has not been systematically explored. This study was conducted to determine whether p16 is a useful parameter in the diagnosis and prognosis of conjunctival melanocytic nevi and melanoma, either independently or as a component of immunohistochemical panels. Sixty-one patients underwent 61 biopsies for conjunctival melanocytic lesions between 2014 and 2018. Pathologic diagnoses were melanoma (n = 25, 41%), nevus (n = 21, 34%), and conjunctival melanocytic lesion of uncertain malignant potential (n = 15, 25%). The biopsies were assessed for expression of p16, SOX10, HMB45, and Ki-67. In a multivariable model, the parameters most predictive of melanoma versus nevus were diffuse HMB45 staining (odds ratio [OR] = 45, confidence interval [CI] = 4.4–457, P = .02] and p16 nuclear H-score≤115 (OR = 9.5, CI = 1.2–77; P = .04). There was no association of p16 expression with melanoma thickness. Next-generation sequencing identified no CDKN2A mutations or copy number alterations in 12 conjunctival melanomas, including the tumors with absent p16 expression. This study demonstrates that p16 immunohistochemical stain is useful in distinguishing conjunctival melanocytic nevi from melanoma, particularly in combination with HMB45. P16 expression does not appear to correlate with CDKN2A status and melanoma thickness.