Background: It is controversial in multiple myeloma (MM) whether early and late responders to therapies have similar clinical outcomes. Daratumumab (DARA) is a human anti-CD38 antibody that has been increasingly used in newly diagnosed MM (NDMM) and relapsed/refractory MM (RRMM). The association between response kinetics to DARA and clinical outcomes remains unexplored.

Methods: Individual-participant data were obtained from phase 3 trials: POLLUX (Dimopoulos, NEJM, 2016), CASTOR (Palumbo, NEJM, 2016), and MAIA (Facon, NEJM, 2019). Patients were divided into early and late response groups based on the median time to the response of interest. Modified PFS (mPFS) and OS (mOS) were calculated from the time of first response of interest. Minimal residual disease (MRD) negativity was defined as less than 10 5 tumor cells by NGS assays.

Results: After a median follow up of 16.1 months, 670 patients achieved a response of very good partial response (VGPR) or better, and 213 achieved MRD negativity. The median time to achieving VGPR or better was similar between NDMM and RRMM (86 vs. 84 days, respectively), while the median time to MRD negativity was longer among NDMM than RRMM (407 vs. 197 days, respectively). Among patients achieving VGPR or better, there was no significant difference of mPFS (HR 1.00, 95%CI 0.69 to 1.44) (fig. a), duration of response (DOR) (HR 1.02, 95%CI 0.68 to 1.53) (fig. b), or mOS (HR 0.98, 95%CI 0.54 to 1.75) (fig. c) between early and late responders. In the subgroup analysis, no significant difference of DOR was observed across all prespecified groups, including sex, age, cytogenetic risk groups, lines of previous therapy, types of measurable disease, NDMM vs. RRMM, prior treatment with autologous hematopoietic cell transplant, immunomodulatory drugs, or proteasome inhibitors. Among patients with NDMM achieving MRD negativity, there was no significant difference of mPFS (p=0.66) (fig. d), DOR (p=0.21) (fig. e) or mOS (p=0.87) (fig. f) between early and late responders. However, among patients with RRMM achieving MRD negativity, late responders had significantly longer mPFS (p=0.038) (fig. g) and DOR (p=0.043) (fig. h) than early responders; mOS was not significantly different (fig. i). In the multivariable Cox analysis among patients achieving MRD negativity, only lower baseline LDH level, NDMM, and IgG type MM were independently associated with later response.

Conclusions: For patients with NDMM or RRMM achieving VGPR or better, early and late responders had similar survival; for patients with RRMM achieving MRD negativity, late responders had significantly longer mPFS and DOR. Our data support that in patients who failed to achieve an early or deep response to daratumumab based regimens, therapies should be continued with the goal of achieving ongoing and stepwise improvement of response.

Figure 1
Figure 1.
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Disclosures

No relevant conflicts of interest to declare.

© 2021 by The American Society of Hematology
2021
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