To evaluate clinical features and risks for transformation of conjunctival primary acquired melanosis (PAM) into melanoma.

Retrospective chart review and Kaplan-Meier estimates of times to PAM enlargement, recurrence, and transformation into melanoma. Main outcome measures: PAM enlargement, recurrence, and transformation into melanoma.

The mean patient age at diagnosis of PAM was 56 years; 62% were female and 96% Caucasian. The conjunctival quadrant(s) affected by PAM and its extent in clock hours were recorded. Initial management included observation in 62%, biopsy combined with cryotherapy in 34%, and other methods in 4%. Of PAM that was observed, Kaplan-Meier estimates at 10 years revealed PAM enlargement in 35% and transformation into melanoma in 12%. Of those that underwent incisional or excisional biopsy, 10-year estimates of PAM recurrence and transformation into melanoma were 58% and 11%, respectively. Progression to melanoma occurred in 0% of PAM without atypia, 0% of PAM with mild atypia, and 13% of PAM with severe atypia. Multivariable analysis revealed that the most significant factor for both PAM recurrence and progression to melanoma was extent of PAM in clock hours.

PAM without atypia or with mild atypia shows 0% progression into melanoma, whereas PAM with severe atypia shows progression into melanoma in 13%. The greater the extent of PAM in clock hours, the greater the risk for transformation into melanoma.