Opposite roles of BAP1 in overall survival of uveal melanoma and cutaneous melanoma

Background: BAP1 germline mutations predispose individuals to a number of cancer types including uveal melanoma (UM) and cutaneous melanoma (CM) which are distinctively different in the oncogenic pathways. BAP1 loss was common in UM and was associated with a worse prognosis. BAP1 loss was rare in CM and the outcome was unclear. Methods: This study used TCGA UM and CM databases for survival analysis for patients with different BAP1 status and mRNA expression levels. Cox regression model was used for adjusting to known prognosis factors. Results: BAP1- (loss or low expression) predicted a poor overall survival in UM (Cox HR = 0.062, logrank p =0.007) but a contrasting better overall survival in CM (HR = 1.69, p =0.009). Multi-covariate Cox regression analysis indicated BAP1 was a significant predictor for overall survival after adjusting for age of diagnosis, presence of ulceration, Breslow depth and CM stages in patients older than 50 years but not in younger patients. Co-expression analysis revealed no shared genes in BAP1 altered UM and CM tumors, further supporting a completely distinctive role of BAP1 in CM and UM. Conclusions: low BAP1 mRNA was significantly associated with a better overall survival in CM patients, in sharp contrast to its tumor suppressor role in UM where low or loss of BAP1 indicated a worse overall survival. Function of BAP1 may be dependent on cellular context.