R2-ISS staging combined with circulating plasma cells improves risk stratification for newly diagnosed multiple myeloma: a single-center real-world study.

We aimed to evaluate if circulating plasma cells (CPC) detected by flow cytometry could add prognostic value of R2-ISS staging. We collected the electronic medical records of 336 newly diagnosed MM patients (NDMM) in our hospital from January 2017 to June 2023. The median overall survival (OS) for patients and R2-ISS stage I-IV were not reached (NR), NR, 58 months and 53 months, respectively. There was no significant difference in OS between patients with stage I and patients with stage II (P = 0.309) or between patients with stage III and patients with stage IV (P = 0.391). All the cases were re-classified according to R2-ISS stage and CPC numbers ≥ 0.05% (CPC high) or<0.05% (CPC low) into four new risk groups: Group 1: R2-ISS stage I + R2-ISS stage II and CPC low, Group 2: R2-ISS stage II and CPC high + R2-ISS stage III and CPC low, Group 3: R2-ISS stage III and CPC high + R2-ISS stage IV and CPC low, Group 4: R2-ISS stage IV and CPC high. The median OS were NR, NR, 57 months and 32 months. OS of Group 1 was significantly longer than that of Group 2 (P = 0.033). OS in Group 2 was significantly longer than that of Group 3 (P = 0.007). OS in Group 3 was significantly longer than that of Group 4 (P = 0.041). R2-ISS staging combined with CPC can improve risk stratification for NDMM patients.