Increased incidence of a second lymphoproliferative malignancy in patients with multiple myeloma--a SEER based study.

BACKGROUND Improving therapies means longer survival for multiple myeloma (MM) patients. We hypothesized that these patients are at an increased risk for a secondary malignancy. OBJECTIVES (i) To investigate the epidemiology and site-specific risk of second primary cancers (SPCs) in patients with MM (ii) To investigate the factors affecting survival in MM patients with SPCs. DESIGN This was a retrospective cohort study employing data available in the US Surveillance Epidemiology and End Results (SEER) database. SUBJECTS Adult patients (>18 years) where MM was the first of two, or more primary cancers, such that the diagnosis of MM and the SPC was separated by at least 1 month. RESULTS The age-adjusted rate SPCs in MM was 0.22 per 100,000 (95% CI=0.05-2.1). The incidence of SPCs was higher in patients aged ≥70 years, men and blacks. Age, gender and race were significant predictors for the occurrence of SPCs in MM. The risk of solid malignancies was significantly decreased (SIR: 0.94, 95% CI=0.89-0.99), while that of lymphohematopoieitc (LAHM) malignancies increased in MM (SIR: 1.68, 95% CI= 1.46-1.92). 5-year relative survival among MM patients with SPCs was higher in blacks (54.6%, 95% CI=49.5-59.4) than whites (53.8%, 95% CI=51.3-56.3) or other races (49.9%, 95% CI=39.8-59.3). Multivariate analysis revealed that race, site of SPC and year of diagnosis were independent predictors of survival among MM patients with SPCs. CONCLUSION MM patients are at a higher risk of a second LAHM.