Lenalidomide plus dexamethasone (LD) is currently the mainstay of treatment for both untreated and relapsed or refractory multiple myeloma (RRMM). Although lenalidomide-associated venous thromboembolism (VTE) is a major clinical concern, its incidence and prognostic impact have not been delineated. In this nationwide retrospective cohort study, we aimed to determine the cumulative incidence of VTE and its prognostic value using two consecutive cohorts of LD-treated RRMM patients: the KMM151 cohort (N = 542) and the HIRA cohort (N = 1559). Data were collected from medical records for the KMM151 cohort and healthcare insurance claims database for the HIRA cohort. Throughout the study period, 24 patients (4.4%) in the KMM151 cohort and 80 patients (5.1%) in the HIRA cohort developed VTE. The cumulative incidence reached a plateau approximately 2 years after LD initiation. The 2-year incidence was 4.9% in the KMM151 cohort and 8% in the HIRA cohort. Higher starting dose of lenalidomide, previous history of VTE, and older age were associated significantly with an increased VTE risk. Early-onset VTE was associated significantly with poor survival. In conclusion, VTE occurred in 5–8% of RRMM patients treated with LD over 2 years, and early-onset VTE was a strong indicator of poor prognosis.
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