Primary Tumor Thickness is a Prognostic Factor in Stage IV Melanoma: A Retrospective Study of Primary Tumor Characteristics

Introduction: Stage IV melanoma exhibits a diverse range of tumor biology from indolent to aggressive disease. Many important prognostic factors have already been identified. Despite this, the behavior of metastatic melanoma remains difficult to predict. We sought to determine if any primary tumor characteristics affect survival following the diagnosis of stage IV melanoma. Methods: All patients diagnosed with stage IV melanoma between January 2003 and December 2012 were identified from the Victorian Melanoma Service database. Retrospective chart review was performed to collect data on primary tumor characteristics (thickness, ulceration, mitotic rate, melanoma subtype, or occult primary). Known and suspected prognostic factors were additionally collected (time to diagnosis of stage IV disease, age, sex, stage, receipt of chemotherapy, and era of recurrence). The effect of primary tumor characteristics on overall survival from the date of diagnosis of stage IV disease was assessed. Results: A total of 227 patients with a median follow-up of 5 years from diagnosis of stage IV disease were identified. Median overall survival of the cohort was 250 days. Of the primary tumor characteristics assessed, only tumor thickness affected survival from diagnosis of stage IV disease, hazard ratio=1.09 (1.02 to 1.16), P=0.008. This remained significant in multivariate analysis, P=0.007. Other primary tumor characteristics did not significantly influence survival. Conclusions: Primary tumor thickness is a significant prognostic factor in stage IV melanoma. Our data suggest that the biology of the primary melanoma may persist to influence the behavior of metastatic disease.

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