New research shows that the presence and number of clonal plasma cells in an autograft are “highly predictive” of posttransplant outcomes in patients with multiple myeloma who have high-risk chromosomal abnormalities.
Oren Pasvolsky, MD, of the University of Texas MD Anderson Cancer Center in Houston; the Rabin Medical Center, in Petah Tikva, Israel; and the Sackler Faculty of Medicine, in Tel Aviv, Israel, and colleagues conducted the research and presented their findings at the Tenth Annual Meeting of the Society of Hematologic Oncology (SOHO).
“Almost all patients with multiple myeloma undergoing an autologous hematopoietic stem-cell transplantation eventually relapse, and the risk is highest in patients with high-risk chromosomal abnormalities,” Pasvolsky and colleagues wrote. “The significance of clonal plasma cells in the autograft has not been clearly established.”
The researchers studied 416 adult patients with multiple myeloma and high-risk chromosomal abnormalities who underwent autologous hematopoietic stem-cell transplantation between 2008 and 2018. The high-risk chromosomal abnormalities were del17p, t(4;14), t(14;16), and 1q21 gain or amplification by fluorescence in situ hybridization. All patients had 8-color next-generation flow cytometry (NGF) performed on the apheresis product to detect clonal plasma cells and were divided into NGF-positive (n=75) and NGF-negative (n=341) groups. The median follow-up was 35.7 months (range, 0.3-139.5 months).
More patients who were NGF-negative for clonal plasma cells (62%) achieved at least a very good partial response compared with patients who were NGF-positive (32%). The 100-day complete response rate was significantly higher for the group of patients who were NGF-negative (19%) than in the group of patients who were NGF-positive (8%; P<.001). The best posttransplant complete response rate was also significantly higher in the group of patients who were NGF-negative (54%) than in the group of patients who were NGF-positive (33%; P<.001).
The rate of posttransplant minimal residual disease negativity was significantly higher in the group of patients who were NGF-negative (57%) than in the group of patients who were NGF-positive (23%; P<.001).
“It’s quite staggering how impactful presence and degree of clonal plasma cells in the autograft are on the outcomes of patients,” Dr. Pasvolsky said at the SOHO meeting. “It was more predictive of outcomes than [minimal residual disease] in bone marrow for these patients.”
The median progression-free survival (PFS) was significantly higher in patients who were NGF-negative (32.1 months) than in patients who were NGF-positive (12.8 months; P<.001), as was the median overall survival (OS) (81.2 months vs 36.4 months; P<.001). In the subset of patients who had a very good partial response or better before transplant, patients who were NGF-positive had reduced PFS (hazard ratio [HR], 3.38; P<.001) and OS (HR, 2.29; P=.013) compared with the NGF-negative group.
A higher clonal plasma cell count in the autograft was associated with reduced response rates (P=.017) and reduced best posttransplant response rates (P=.048). A higher number of clonal plasma cells in the autograft was also predictive of reduced PFS (HR, 1.50; P=.006) and worse OS (HR, 1.35; P=.007) in a multivariable analysis.
“Both the presence and the number of [clonal plasma cells] in the autograft were highly predictive of posttransplant outcomes, including PFS and OS in patients with [high-risk chromosomal abnormalities],” Dr. Pasvolsky and colleagues concluded. “Novel strategies for ex-vivo purging of [clonal plasma cells] could potentially improve patient outcomes.”
Pasvolsky O, Milton D, Rauf M, et al. Impact of clonal plasma cells in autografts on the outcome of high-risk multiple myeloma patients undergoing autologous hematopoietic stem cell transplant. Poster MM-403. Presented at the Tenth Annual Meeting of the Society of Hematologic Oncology; September 28-October 1, 2022; Houston, TX.