Cytoplasmic Pin1 expression is increased in human cutaneous melanoma and predicts poor prognosis

The prolyl isomerase Pin1 is widely over-expressed or over-activated in cancers and promotes tumorigenesis. The authors investigated the expression level of Pin1 and analyzed the prognostic value of Pin1 expression using a large-scale melanoma tissue microarray study. Two independent sets of tissue microarrays were employed, including 114 melanoma cases in the discovery set and 424 in the validation set (538 cases in total), 32 normal nevi and 86 dysplastic nevi 118 cases of nevi. The subcellular Pin1 expression in different stages of melanocytic lesions and its prognostic significance were studied. High expression (IRS 0-8) of cytoplasmic Pin1 was observed in 3.13%, 8.33%, 16.49% and 22.76% of the biopsies in normal nevi, dysplastic nevi, primary melanoma and metastatic melanoma, respectively. Significant differences for cytoplasmic Pin1 staining were observed between normal nevi and metastatic melanoma (P = 0.011, χ² test), between dysplastic nevi and primary melanoma (P = 0.046, χ² test) and between dysplastic nevi and metastatic melanoma (P = 0.016, χ² test). Kaplan-Meier survival analysis showed that increased cytoplasmic Pin1 expression was associated with a worse 5-year melanoma-specific survival of melanoma (P < 0.001) and metastatic melanoma patients (P = 0.004). Multivariate Cox regression analysis showed that cytoplasmic Pin1 expression is an independent prognostic factor in melanoma. Our data indicate that cytoplasmic Pin1 plays an important role in melanoma pathogenesis and progression, and serve as a potential prognostic marker for melanoma.