p16ink4a Expression in Benign and Malignant Melanocytic Conjunctival Lesions

Acquired conjunctival melanocytic lesions include nevi, primary acquired melanoses (PAMs), and melanomas. Conjunctival melanoma is a malignant melanocytic neoplasm with a high metastasis and mortality rate. Usually, the diagnosis can be achieved only with routine microscopic analysis, but in some cases, the samples are small or have artifacts. In these cases, complementary studies will be helpful, but currently, there are no well-understood or studied complementary methods. Objective. To analyze the immunohistochemical expression of p16 in conjunctival melanocytic lesions and to assess its potential for differentiating between benign and malignant melanocytic lesions. Methods. Immunohistochemical study against p16ink4a (p16) was performed on paraffin-embedded sections on 45 melanocytic lesions (9 melanomas, 19 nevi, and 2 PAMs with atypia and 15 without atypia). Expression was scored according to the German immunoreactive score (IRS). Results. Expression of p16 IRS differed between nevi, PAMs, and melanomas. The mean IRS for melanomas was 3.3 +/- 1.8 and was lower than those for nevi (7.63 +/- 3.24; P < .05), PAM with atypia (12 +/- 0; P < .05), and PAM without atypia (11 +/- 1.69; P < .05). Lesions with infiltration depths lower than 2 mm showed higher levels of p16. There were no differences between favorable and unfavorable locations. Conclusion. p16 Expression in conjunctival melanocytic lesions showed an expression similar to that in skin and seems to be a good marker to differentiate nevi and PAMs from melanomas. However, additional studies of larger series and follow-up are needed to confirm these findings.