Efficacy of elotuzumab for multiple myeloma in reference to lymphocyte counts and kappa/lambda ratio or B2 microglobulin.

Novel therapeutic drugs have dramatically improved the overall survival of patients with multiple myeloma. We sought to identify the characteristics of patients likely to exhibit a durable response to one such drug, elotuzumab, by analyzing a real-world database in Japan. We analyzed 179 patients who underwent 201 elotuzumab treatments. The median time to next treatment (TTNT) with the 95% confidence interval was 6.29 months (5.18-9.20) in this cohort. Univariate analysis showed that patients with any of the following had longer TTNT: no high risk cytogenic abnormalities, more white blood cells, more lymphocytes, non-deviated κ/λ ratio, lower β2 microglobulin levels (B2MG), fewer prior drug regimens, no prior daratumumab use and better response after elotuzumab treatment. A multivariate analysis showed that TTNT was longer in patients with more lymphocytes (≥ 1400/μL), non-deviated κ/λ ratio (0.1-10), lower B2MG (< 5.5 mg/L) and no prior daratumumab use. We proposed a simple scoring system to predict the durability of the elotuzumab treatment effect by classifying the patients into three categories based on their lymphocyte counts (0 points for ≥ 1400/μL and 1 point for < 1400/μL) and κ/λ ratio (0 points for 0.1-10 and 1 point for < 0.1 or ≥ 10) or B2MG (0 points for < 5.5 mg/L and 1 point for ≥ 5.5 mg/L). The patients with a score of 0 showed significantly longer TTNT (p < 0.001) and better survival (p < 0.001) compared to those with a score of 1 or 2. Prospective cohort studies of elotuzumab treatment may be needed to validate the usefulness of our new scoring system.