P-357: Outcomes of multiple myeloma patients with prior solid tumors undergoing an autologous transplant

Introduction: Autologous hematopoietic stem cell transplantation (autoHCT) remains standard care for patients with multiple myeloma (MM). Prior solid tumor is the highest scoring variable in the hematopoietic cell transplantation specific comorbidity index (HCT-CI), which is used to estimate mortality risk after transplant. There are limited data on the impact of prior solid tumors on the outcomes of MM patients undergoing autoHCT.

Methods: Single-center retrospective study in a large tertiary referral center. We included all consecutive MM patients who received upfront autoHCT between 1997 and 2021 and divided them into two groups: with or without prior solid tumor (PSM+ and PSM- groups, respectively). High risk cytogenetic abnormalities were defined as t(4;14), t(14;16), del(17p), and 1q21 gain or amplification by fluorescence in situ hybridization (FISH) analysis. Primary endpoints were progression-free survival (PFS) and overall survival (OS).

Results: 2853 MM patients were included in the study, of whom 274 were in the PSM+ group, the most prevalent being prostate cancer (n=81), breast cancer (n=50), melanoma (n=31), renal cell carcinoma (n=19) and colorectal cancer (n=13). Patients in the PSM+ group were older than those in the PSM- group (67 vs. 60 years; p< 0.001), more often male (66% vs. 58%; p=0.010) and more often transplanted after the year 2010 (78% vs. 69%; p=0.003). There was a trend towards increased incidence of high-risk cytogenetic abnormalities in patients in the PSM+ group (30% vs. 24%; p=0.06).

There was no significant difference in pre-transplant (p=0.33), day 100 post-transplant (p=0.35) and best post-transplant (p=0.27) hematological responses between the PSM+ and PSM- groups. Similarly, there was no significant difference in pre-transplant (p=0.34) or best post-transplant (p=0.44) minimal residual disease (MRD) status between the two groups.

There was no difference in PFS between the PSM+ and the PSM- groups (36.7 months vs. 39.9 months; p=0.31). In contrast, patients in the PSM+ group had worse OS compared to those in the PSM- group (81.3 months vs. 104 months; p=0.020). Within the PSM+ group, median OS for specific cancer subtypes were: thyroid cancer not reached; colorectal cancer 154.9 months; renal cell carcinoma 85.0 months; melanoma 81.3 months; prostate cancer 80.1 months; breast cancer 73.5 months; and bladder cancer 65.5 months. In multivariate analysis, prior solid tumor retained its negative predictive impact on OS (HR 1.34, 95% CI 1.07-1.68; p=0.011).

102 patients in the PSM+ group died during follow up. The most common cause of death was progression of MM (77/102, 75%); 3 patients died of their prior malignancy (lung cancer, breast cancer and melanoma, 1 each), and 7 died of a second primary malignancy that developed following transplant.

Conclusions: Patients with MM and a prior solid tumor had inferior overall survival after an autoHCT, confirming its adverse prognostic impact on transplant outcomes.