Expression of PIWIL3 in primary and metastatic melanoma

The PIWI-interacting RNA machinery in malignant melanoma (MM) has not been sufficiently studied. We aimed to investigate the PIWIL3 expression profiles in primary melanomas and metastases of MM including a correlation with clinical data. We studied 161 primary melanomas, 45 lymph node metastases, and 16 distant metastases of 183 patients with MM. We used immunohistochemistry to assess PIWIL3 protein expression in situ. The relationship between the immunoreactivity of PIWIL3 and clinical data was statistically evaluated. We observed a significantly (P = 0.000059) higher median immunoreactivity score in primary melanomas (4.9; range, 0.1-6), lymph node metastases (5.1; range, 3.3-6), and distant metastases (5.6; range, 4.5-6). PIWIL3 was expressed significantly higher (P = 0.0002) in primary nodular melanomas and acral melanomas (5.2; range, 3.4-6) when compared to other melanoma subtypes (4.7; range, 0.1-6). On univariate analysis, a significant positive correlation was observed between primary melanoma PIWIL3 expression and tumor thickness (r = 0.2; P = 0.014). On univariate and multivariate analysis, PIWIL3 did not prove to be an independent predictor for melanoma relapse or death. Our data indicate that PIWIL3 protein expression is elevated in more aggressive primary MM and metastatic disease. As also observed in other malignancies, PIWIL3 seems to play a role in MM progression.