Cancer history and second cancer risk in polycythemia vera and essential thrombocythemia.

Patients with myeloproliferative neoplasms (MPN), including polycythemia vera (PV) and essential thrombocythemia (ET), have an increased risk of second cancers (SC), although determinants of risk remain incompletely defined. We retrospectively analyzed 1968 consecutive patients with PV or ET (median follow-up 11.2 years) to identify predictors of SC. Cumulative incidence functions were estimated using competing-risk methodology, and predictors were assessed using Fine-Gray regression. During follow-up, SC occurred in 404 patients (20%), with non-melanoma skin cancer (NMSC) representing the most frequent subtype. In multivariable models including all cancer types, prior cancer (sHR 2.02, p < 0.001), older age (per 10 years: sHR 1.20, p < 0.001), male sex (sHR 1.39, p = 0.002), and hyperlipidemia (sHR 1.41, p = 0.003) independently predicted SC. After excluding NMSC, prior cancer remained associated with SC risk (sHR 1.48, p = 0.048). Notably, prior NMSC strongly predicted subsequent NMSC (sHR 6.48, p < 0.001), followed by prior non-NMSC cancer (sHR 2.11, p < 0.001), age (sHR 1.29, p < 0.001), and male sex (sHR 1.43, p = 0.018). TET2 mutations showed a borderline association with NMSC risk (sHR 1.73, p = 0.055), while hydroxyurea was not associated with SC, with a non-significant trend toward increased NMSC risk (sHR 1.82, p = 0.110). These findings support risk-adapted cancer surveillance in PV and ET, with particular emphasis on regular dermatologic monitoring.