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INTRODUCTION/BACKGROUND:Second primary malignancies (SPMs) are long-term complications in cancer survivors. Mucosa-associated lymphoid tissue (MALT) lymphomas are indolent extra-nodal marginal zone lymphomas, the majority of which typically have long-term survival. In this study, we investigated the incidence and pattern of SPMs in adult patients diagnosed with MALT lymphomas between January 2000 and December 2016. METHODS:Using the SEER-18 database and multiple primary standardized incidence ratio (MP-SIR) session of SEER stat software for statistical analysis, we assessed SPMs in MALT lymphomas. RESULTS:During this time, a total of 12,500 cases of MALT lymphomas were diagnosed, of which 1466 patients developed 1626 SPMs (O/E ratio: 1.48, 95% CI:1.41-1.55, P<.001). The median latency period for development of SPMs was 54 months (range 6-201 months). Secondary non-Hodgkin lymphomas, as defined by SEER as distinct from the primary lymphoma, was the most common SPM with 299 cases, followed by lung cancer (O/E ratio: 6.15, 95% CI:5.47-6.89, P<.0001). There were 898 SPMs that developed between 6- 59 months (O/E ratio: 1.47, 95% CI:1.37-1.57, P<.0001) and 728 after 60 months latency (O/E ratio: 1.5, 95% CI:1.39-1.61, P<.0001) after diagnosis of the primary MALT lymphomas. An increased incidence of both solid and hematologic cancers occurred in patients as early as 6 months after diagnosis of MALT lymphoma. CONCLUSION/CONCLUSIONS:These findings indicate that despite the indolent nature of most MALT lymphomas, there is an increased risk for SPMs warranting long-term follow up.