Incidence Of Second Primary Malignancy (Spm) In Patients With Mucosa-Associated Lymphoid Tissue Lymphoma (Maltoma).

e20043 Background: MALTomas are extranodal marginal zone lymphomas that arise from B cells in various mucosal lymphoid tissue and are typically indolent. Patients with MALTomas may be at risk for additional cancers due to their long-term survival following treatment, however the incidence of SPM in MALTomas in the U.S. has not been previously described. Methods: Adults with MALT lymphoma were identified using the 2000-2016 SEER-18 database. SPM was defined as tumors diagnosed ≥6 months and up to x months from lymphoma diagnosis. SEER*stat was used to calculate SPM by multiple primary standardized incidence ratio based on observed (O) and expected (E) cases. The expected cases of new cancers of specific types were estimated by assuming that incidence rates for new primary tumors corresponded to sex, age, and calendar time–specific SEER rates for similar invasive primary cancers and applying those rates to the accumulated person-years (PYR) of observation. Excess absolute risk (EAR) of malignancy per 10,000 PYR at risk was calculated as ([O − E]/PYR) × 10,000. Results: As summarized in the table, 12,500 patients were diagnosed with MALT lymphoma of which 1466 (11.8%) developed 1626 SPMs (O/E rate 1.5, 95%CI 1.4-1.5, P < 0.001, EAR 70.4). Median latency period was 54 months (range 6 - 201). Non-Hodgkin lymphomas at separate tissue sites were the most common SPM, with 299 documented cases (O/E rate 6.2, 95%CI -5.4-6.8, P < 0.001, EAR 33.4). Between 6-24 months from MALToma diagnosis, head and neck, renal cell, liver, and anal cancers were increased, while after 24 months, gastric and small bowel cancers, CLL, ALL, and myeloma were increased compared to the general population of the same age group. Conclusions: There is distinct pattern of SPM among patients with MALT lymphoma in within and after 2 years from diagnosis, with an increased incidence compared to the general population. Consider the median latency, SPM may be due in part to the long-term survival and relatively older age of this population. [Table: see text]