Impact of Multiple High-Risk Cytogenetic Abnormalities on the Survival Outcomes of Patients with Primary Plasma Cell Leukemia

INTRODUCTION Primary plasma cell leukemia (pPCL) is a rare and aggressive form of multiple myeloma (MM) with poor survival outcomes. Fluorescence in situ hybridization (FISH) evaluation is essential for the initial risk stratification in MM, and the presence of multiple high-risk (HR) cytogenetic abnormalities by FISH portends a worse prognosis in MM. We have previously observed that the presence of HR cytogenetic abnormalities by FISH at diagnosis is known to confer a poor overall survival (OS) in patients with pPCL. However, less is known about the cumulative effect of multiple HR cytogenetics abnormalities compared to a single HR cytogenetic abnormality on the OS outcomes of patients with pPCL. AIM To evaluate the prognostic implications of additive HR cytogenetics abnormalities by FISH in patients with pPCL treated with novel agents. METHODS We evaluated patients with newly diagnosed pPCL at the Mayo Clinic Comprehensive Cancer Center from 2014 - 2023 that received induction with novel agent combinations. pPCL was defined as patients meeting the diagnostic criteria for MM with 5% or more circulating plasma cells (cPCs) present on morphologic evaluation of their peripheral blood smear. HR cytogenetics abnormalities by FISH was defined by the presence of any one of the following: 1q gain/amplification, t(4;14), t(14;16), t(14;20), and del(17p). Time to next treatment (TTNT) and OS analysis were performed using the Kaplan-Meier method, and differences were assessed using the log-rank test. Statistical analyses were performed using the SAS biostatistical software JMP 17.0.1 (SAS Institute Inc). RESULTS We included 89 patients with newly diagnosed pPCL who received novel agents as first-line therapy between 2014 to 2023. The median follow-up was 45 months (95% CI: 35 - 65). At diagnosis, the median bone marrow plasma cell content was 80% (Range: 10 - 100), and the median cPC% on the peripheral smear was 21% (range: 5 - 85). There were 51 patients (59%) who had 20% or more cPCs on their peripheral smear. There was a preponderance of pPCL patients who had t(11; 14) as their primary cytogenetic abnormality (43%). The median lines of therapy received were 2 (Range: 1 - 9). There were 12 (13%) patients who received intensive induction therapy containing continuous infusional chemotherapy regimens at the onset of their diagnosis. Of the remaining patients, 35 (45%) were treated with a quadruplet (anti-CD38 antibody, proteasome inhibitor and immunomodulator), 24 (31%) with a triplet (proteasome inhibitor and immunomodulator) and 18 (23%) with a doublet (proteasome inhibitor only). The median OS for all pPCL patients in this cohort was 47 months (95% CI: 37 - 100). However, when stratified by cytogenetic risk, the median OS was 101 months (95% CI: 57 - NR) for those patients without any HR cytogenetic abnormalities (N = 24, 27%) vs. 37 months (95% CI: 22 - 63) for those with one or more HR cytogenetic abnormalities (N = 65, 73%) (P = 0.006). Of the patients with any HR cytogenetic abnormalities, 33 (36%) had one HR cytogenetic abnormalities and 32 (34%) had two or more HR cytogenetic abnormalities. The median OS for patients with one compared to two or more HR cytogenetic abnormalities were 47 (95% CI: 38 - 111), and 22 (95% CI: 17 - 37) months, respectively (P = 0.031). The median TTNT was 22 months (95% CI: 16 - 58) for those patients without any HR cytogenetic abnormalities vs. 16 months (95% CI: 9 - 21) for those with one or more HR cytogenetic abnormalities (P = 0.09). The median TTNT from the time of diagnosis for pPCL patients with one compared to two or more HR cytogenetic abnormalities were 18 (95% CI: 6 - 41) and 16 (95% CI: 10 - 19) months, respectively (p = 0.247). CONCLUSION Patients with pPCL with more than one HR cytogenetic abnormality had an inferior OS compared to those with only one HR cytogenetic abnormality, implicating the additive adverse effects of multiple HR cytogenetics abnormalities. In contrast, patients with pPCL without any HR cytogenetic abnormalities had a relatively long median OS (over 100 months).