Survival in mantle cell lymphoma patients burdened by a second primary malignancy.

Second primary malignancies (SPMs) increasingly affect mantle cell lymphoma (MCL) survivors. In nationwide Danish and Swedish cohorts (2000-2020), we evaluated overall survival among MCL patients with SPMs versus matched non-lymphoma individuals with comparable malignancies and MCL patients without SPMs, respectively. Of 3094 MCL survivors, 19% in Denmark and 15% in Sweden developed an SPM, with a median of three years from MCL diagnosis to first SPM. MCL patients with SPMs had about double the mortality risk compared with non-lymphoma counterparts (pooled HR 2.1, 95% confidence interval (CI) 1.3-3.5), and worse survival than MCL patients without SPMs (pooled HR 1.6, 95% CI 1.4-1.9). In Swedish MCL patients with SPMs, deaths were attributed to subsequent hematologic malignancies (9%), solid cancers (14%), primary MCL (23%), non-cancer causes (11%), with 40% still alive. Development of SPMs in MCL is associated with substantially higher mortality, supporting long-term surveillance and proactive management of late complications.