Clinical outcome of ≥2% circulating tumor cells in newly diagnosed multiple myeloma: insights from a multicenter study

PURPOSE: Previous studies have shown that ≥2% circulating tumor cells (CTCs) in multiple myeloma are associated with a prognosis similar to primary plasma cell leukemia. This study aims to examine this ultra-high-risk patient subset and evaluate their clinical outcomes in a real-world clinical setting. METHODS: morphological assessment on peripheral blood smears, using a 2% cutoff to stratify patients into <2% and ≥2% CTCs groups. We then evaluated clinical outcomes across these groups. RESULTS: Patients with ≥2% CTCs constitute an ultra-high-risk subgroup, with outcomes resembling those of primary plasma cell leukemia. Survival outcomes improved for patients receiving daratumumab-based quadruplet therapy. Single autologous stem cell transplantation (ASCT) partially improved outcomes for patients with ≥2% CTCs. Achieving complete remission (CR) after induction treatment did not confer a better prognosis for this population. Furthermore, one high-risk cytogenetic abnormality (HRA) worsened outcomes in the <2% CTC group, while ≥2 HRA were associated with poorer outcomes in the ≥2% CTC group. Concurrent 1q21+ and other HRA further conferred a worse prognosis. In de novo extramedullary extraosseous (EME) multiple myeloma, defined as patients presenting with soft tissue or visceral plasmacytomas not connected to bone at initial diagnosis, ≥2% CTCs remained a strong predictor of poor prognosis. CONCLUSION: Our study suggests that patients with ≥2% CTCs represent a distinct ultra-high-risk subgroup in multiple myeloma and warrant separate consideration. VRD, IRD, DVRD, and DRD were reliable choices as frontline therapies for patients with <2% CTCs. Daratumumab-based quadruplet therapy may be a promising option for patients with ≥2% CTCs. Further research should continue to explore this specific aspect in greater depth.