Increased incidence of another cancer in myeloproliferative neoplasms patients at the time of diagnosis.

Several studies have reported an increased incidence of coexistent cancer in patients with myeloproliferative neoplasms (MPN), and myelosuppressive treatment has been speculated to be one of the causes. In this study, we have concentrated on malignancies diagnosed before the MPN diagnosis to eliminate the possible influence of MPN treatment. The patients were recruited from the Swedish and Norwegian cancer registries. One thousand seven hundred and 45 patients from the Swedish MPN Quality Registry and 468 patients from the Norwegian National Cancer Registry were included in this study covering a 3-yr period. The results show that primary concurrent cancer is higher among patients with MPN compared to the general population. When pooled together, the Swedish and the Norwegian cohort showed increased prevalence of all types of cancer in general compared with the general population, standard prevalence ratio (SPR) of 1.20 (95% CI 1.07-1.34). Significantly high SPRs were reached for skin malignant melanoma [1.89 (95% CI 1.33-2.62)], prostate cancer [1.39 (95% CI 1.11-1.71)], and hematologic cancer [1.49 (95% CI 1.00-2.12)]. In the polycythemia vera group, the risk of having prior malignant melanoma of the skin was significant, with an SPR of 2.20 (95% CI 1.17-3.77). For patients with essential thrombocythemia and primary myelofibrosis, no significant risks were found. Coexisting cancers have a high impact on the treatment strategies of MPN, as it narrows down the treatment options. Chronic inflammation, as a common denominator of MPN with other cancers, can catalyze each other's existence and progression.