Expression of p53 protein in malignant melanoma: clinicopathological and prognostic implications

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Abstract
In the present study, we investigated the expression of the tumour suppressor protein p53 in 1 primary and 43 metastatic malignant melanomas by immunohistochernistry, and correlated the findings with clinicopathological parameters such as histological melanoma subtype, thickness of primary melanomas (Breslow thickness) and patient outcome. In primary melanomas, the polyclonal anti‐p5 3 antibody CM‐1 detected immunoreactivity in 70% of the lesions, predominantly in the cytoplasm. Signals were observed in this cellular compartment in 57% of the melanomas, whereas in 32% nuclear p53 over‐expression was detected. Immunohis‐tochemistry, using the monoclonal antibody DO‐1, revealed lower staining frequencies. However, both antibodies showed congruent results in approximately 80% of the cases. Overall, immuno‐reactivity was observed in 73% of superficial spreading melanomas, but only in 52% of lentigo maligna melanomas. This difference (P<0.001) was mainly due to a lower frequency of cytoplasmic immunoreactivity (P<0.002). There was no difference with respect to cytoplasmic and nuclear immunoreactivity between thin (<1 mm thickness) and thicker primary melanomas. Staining frequencies detected in metastatic lesions seemed to be lower than in primary tumours. In 103 primary melanomas, follow‐up data for at least 5 years were available. In 71% (54 of 76) of the primary melanomas which did not recur, and in 78% (21 of 27) of tumours with subsequent metastases, p53 over‐expression was detected by CM‐1. However, this difference was not statistically significant. The results of the present study indicate that immunoreactivity to anti‐p53 antibodies is a common observation in malignant melanomas, with staining signals predominantly found in the cytoplasm of cells. The observation of similar staining frequencies in thin, thick and metastatic lesions indicates that p53 over‐expression is an early event in the pathogenesis of malignant melanoma. However, the immunohistochemical detection of p53 in primary melanomas is not related to prognosis.