Platelet count correlates with stage and predicts survival in melanoma.

Cancer is a chronic inflammatory state which is often associated with increased platelet counts. Cancer cells induce thrombopoiesis and activate platelets, which in turn facilitate cancer invasion and metastasis. In this study, we investigate the correlation between platelet counts with each of stage and overall survival in melanoma. This is a retrospective cohort study of 642 melanoma patients diagnosed or treated at a tertiary medical center between 2000 and 2016. Multivariable analysis adjusted for age, sex, stage, and treatment modality. Using multivariable analysis, patients with thrombocytosis around time of diagnosis were more likely to present with distant metastasis (Prevalence Ratio 3.5, 95% CI 2.35-5.22). In patients with metastatic disease and in all stages combined, thrombocytosis predicted decreased 5-year overall survival in univariate and multivariable analysis, and this was most pronounced during the first year after diagnosis. Finally, we show that mice with thrombocytopenia due to the lack of heat shock protein gp96 in their megakaryocytes are protected from melanoma dissemination to the lungs. These findings are concordant with preclinical studies showing a role for platelets in cancer metastasis and suppression of antitumor immunity, further supporting targeting platelets as an adjuvant to immunotherapy in melanoma.