Melastatin expression determined by chromogenic in situ hybridization (CISH) in primary cutaneous melanoma

Abstract

7517 Background: Using a radioactive in situ hybridization method on primary melanoma (PM), loss of the melastatin (MLSN-1) mRNA expression has been found to have independent prognostic significance. In this study, we examined whether a new non-radioactive chromogenic ISH (CISH) method to evaluate melastatin expression would similarly predict PM outcome. Methods: Melastatin mRNA was evaluated by CISH on formalin fixed paraffin embedded tissues from 109 PM patients with localized disease (AJCC stages I and II). PMs were classified as having complete or partial down regulation of MLSN compared to internal control intraepidermal melanocytes. MLSN status was compared with standard prognostic factors over a mean clinical follow-up of 58 months with a range of 2 to 225 months. Results: On univariate analysis, partial or complete loss of MLSN expression, found in 32% and 27% of PM respectively, correlated with disease free survival (DFS) (p<.0001). AJCC stage (p<.0001), thickness (p<0.0001), ulceration (p=0.007), mitotic count (p=0.008), and Clark's level (p=0.04) were also significant factors. On multivariate analysis, partial or complete loss MLSN expression was the only independent prognostic factor (p<0.0001). PMs with preserved MLSN expression featured a 100% DFS in contrast to PMs with MLSN loss which had a 35% 10 year DFS. Down-regulation of MLSN expression significantly correlated with advanced AJCC stage, high mitotic count and brisk tumor infiltrating lymphocytic host response (TILs). PMs with MLSN loss and low TILs had a 5 year DFS of 51% compared to a 79% DFS for MLSN preservation and high TIL PMs (p=0.08). Conclusions: MLSN status in PM can readily be measured by CISH and reproduces past RISH findings highlighting that down-regulation of MLSN mRNA in PM is a prognostic biomarker for metastasis that is independent of other classic prognostic factors. MLSN determination by CISH has the potential to supplement current, standard prognostic assessment of primary cutaneous melanomas in routine clinical practice. Author Disclosure Employment or Leadership Consultant or Advisory Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Millennium Pharmaceuticals Millennium Pharmaceuticals Millennium Pharmaceuticals