Prognostic Impact of Residual Clonal Plasma Cell Proliferation After Autologous Stem Cell Transplantation in Multiple Myeloma

By
Tamer Hellou
Daniel G. Packard
Maximilian J. Steinhardt
Shaji K. Kumar
Angela Dispenzieri
Saurabh Zanwar
Shinichiro Suzuki
Estefania Gauto Mariotti
Dragan Jevremovic
Horatiu Olteanu
Pedro Horna
Gregory Otteson
Francis K. Buadi
David Dingli
Suzanne R. Hayman
Prashant Kapoor
Nelson Leung
Joselle Cook
Nadine Abdallah
Moritz Binder
Rahma Warsame
Taxiarchis V. Kourelis
Ronald S. Go
Yi Lin
Eli Muchtar
S. Vincent Rajkumar
Wilson I. Gonsalves
Morie A. Gertz
November 13, 2026

Blood Cancer Journal

Objective:

To assess whether post-ASCT clonal plasma cell S-phase and changes in S-phase from transplantation to post-transplant assessment are associated with outcomes in multiple myeloma.

Approach:

Study design and cohort: Retrospective Mayo Clinic study of 1,055 patients who underwent ASCT within one year of diagnosis between January 2013 and August 2024.
Measurement: Flow cytometry measured clonal plasma cell S-phase in post-ASCT marrow samples collected around day +60 or +100. S-phase was categorized as <2% or ≥2%; samples without enough clonal cells for reliable measurement were classified as non-assessable (N/A).
Analysis: Landmark PFS and OS were compared across S-phase categories and, in 160 patients with paired measurements, across four patterns of change. Multivariable Cox models assessed associations with survival.

Key Findings:

Post-ASCT S-phase was quantifiable in 172 patients (16.3%); 883 (83.7%) were non-assessable because clonal plasma cells were absent or insufficient.
Median PFS was 95 months for N/A, 37 months for S-phase <2%, and 11 months for S-phase ≥2% (p < 0.0001).
Median OS was not reached for N/A or S-phase <2%, compared with 53 months for S-phase ≥2% (p < 0.0001).
Among 160 patients with paired measurements, median PFS was 37 months for low-low, 22 months for high-low, 17 months for low-high, and 7 months for high-high (p < 0.001). Median OS was not reached for low-low and high-low, and was 83 months for low-high and 25 months for high-high (p < 0.001).

Interpretation:

In this cohort, elevated post-ASCT clonal plasma cell S-phase and persistently elevated or newly elevated S-phase were associated with shorter survival. The authors describe S-phase as complementary to residual disease burden assessment because it measures proliferative behavior.

Limitations:

The study was retrospective and conducted at a single center.
S-phase was quantifiable in a minority of patients; most samples were non-assessable because clonal plasma cells were absent or insufficient.