Evaluation of dna copy number changes and chromosomal aberrations in melanocytic tumors by fluorescence ın-situ hybridization method, ınvestigation of ıts differential diagnosis and prognostic value

Introduction-aim: Melanocytic tumors characterized by neoplastic proliferation of melanocytes and have highly wide and heterogeneous spectrum morphologically and genetically. Melanoma responsible for almost 60% of fatal skin tumors. Therefore, molecular studies for etiopathogenesis increasingly gain importance. In our study, we aimed to research the diagnostic value of four-colored fluorescent in situ hybridization method targeted of 6p25, 6q23, 11q13 and centromeric region of chromosome sixth at particularly melanocytic tumors which have diagnostic challenge. We aimed to determine differences of chromosomal aberrations in melanocytic nevus, displastic nevus, non-metastatic melanoma and metastatic melanoma and its place at biological behavior of malignant melanoma, comparing conventional morphological and prognostic criteria.Material and Method: In this study, we involved 74 melanocytic lesions, which diagnosed at Cukurova University School of Medicine Pathology Department. 17 cases (23%) had benign feature, 28 cases (38%) had borderline feature, 29 cases (39%) had malign feature. Borderline and malign lesions were selected from among the patients who have clinical follow-up. Fluorescence in situ hybridization procedure was performed on 3µm thickness sections of formaline fixed-paraffin embedded tissues taken from these cases. The results were examined by fluorescence microscope and numeric value of different four colors corresponding to copy numbers of genes were recorded.Results: Fluorescence in situ hybridization was negative in all of 17 melanocytic nevi cases; positive in 6 of 19 cases of borderline lesions which have diagnostically challenging; positive in 10 of 11 non-metastatic melanoma and positive in all of 18 metastatic melanoma cases. The evaluation of test results were based on histopathological diagnosis as clearly benign and malignant lesions and were based on the characteristics of lesions that determined according to clinical behavior for borderline melanocytic lesion. Test sensitivity was 98,5% and specifity was 100%. Quantitative values of signal parameters compared as pairs in benign, borderline, non-metastatic and metastatic groups. All parameters, except of 6q23 loss had statistically significant difference when compared benign and borderline groups, borderline and non-metastatic groups, but there was no statistically significant difference between non-metastatic and metastatic melanom. Abnormal 6p25 and loss of 6q23 had strong correlations to prognosis, and 11q13 and 6q23 amplifications had weakly correlations to prognosis. 6p25 positivity was observed frequently at acral region (83,3%) and lower extremity (75%). Significant correlation were determined between 6p25 abnormality and 11q13 amplification with tumor diameter (p=0,001, p=0,046 respectively). There was significant correlation between 6p13 amplification and mitosis was observed (p=0,046).Conclusion: In our study, we showed that abnormality and amplification of 6p25, and amplification of 6q23 and 11q13 play an active role in earlier stages of carcinogenesis, but those were not related to metastatic potential of tumor. We thought that 6q25 is a strong prognostic parameter which is correlated to tumor diameter, however loss of 6q23 is the prognostic parameter that is independent from Breslow length, tumor diameter, ulceration and mitosis. 11q13 and 6p23 amplification were in the opinion of the vaguely prognostic parameters that correlated only to tumor diameter and mitosis respectively. Fluorescence in-situ hybridization is highly sensitive and specific method especially for diagnostic evaluation of challenging melanocytic lesions and can also be useful in patient clinical follow-up for prognosis.