Factors associated with over and underuse of response evaluation in elderly myeloma patients.

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e19518 Background: Most patients with multiple myeloma (MM) have detectable monoclonal protein. While guidelines do not specify the frequency of lab testing for response evaluation, most MM clinical trials perform monthly assessment. We examined the use of 4 serologic tests – protein electrophoresis (SPEP), immunofixation (IFE), quantitative immunoglobulins (QIG), and free light chain (FLC) in newly-diagnosed MM patients. Methods: We identified patients age ≥65 with MM (ICD-O 34000) in the Surveillance, Epidemiology and End Results (SEER)-Medicare database from 2000-2013. Patients were required to have bone marrow biopsy within 6 months of diagnosis, and taken chemotherapy approved for MM. Use of a test was defined as having ≥1 instance of its CPT code within 12 months of diagnosis. Patients with > 12 instances were defined as overusers. Multiple instances of a test on the same date were counted once. Multivariable logistic regression models using covariates including: age and year at MM diagnosis, race, marital status, Charlson comorbidity, chemotherapy use, number of hospitalizations and oncology office visits within 12 months of diagnosis, were developed to examine associations with overuse. Results: Among 6,214 identified patients, users were: SPEP 5,532 (89%), IFE 4,745 (76%), QIG 5,524 (89%), and FLC 3,864 (62%). The median (interquartile range) times each test was used in the first year following diagnosis were: SPEP 6 (3-10), IFE 3 (2-7), QIG 6 (3-10), FLC 5 (2-9). The numbers of overusers were: SPEP 721 (13%), IFE 265 (6%), QIG 498 (9%), FLC 350 (9%). 231 (4%) patients were overusers of 2 tests. Factors associated with overuse common to all 4 tests were: younger age at diagnosis (eg, SPEP: odds ratio (OR) 2.0 for aged 65-74 vs ≥85; P < .001), more oncology office visits (eg, QIG: OR 2.2 for > 15 vs 0-6; P < .001), and use of combination chemotherapy (eg, SPEP: OR 2.2 for proteasome inhibitor + immunomodulatory drug (IMID) vs those on IMID ; P < .001). Conclusions: In our Medicare population, patients on average underwent response evaluation much less often than monthly, but we also found overuse. Further investigation of the use of these tests is warranted given their central importance to MM care and their cumulative financial cost.