Complete blood and urine paraprotein tests as response assessments in multiple myeloma patients treated with bortezomib, cyclophosphamide, and dexamethasone

Abstract Background This study assessed the effect of standardized efficacy markers on prognosis in patients with newly diagnosed multiple myeloma (MM) during the induction phase of treatment with bortezomib, cyclophosphamide, and dexamethasone (BCD). Methods We retrospectively analyzed clinical data in 197 newly diagnosed MM patients treated with BCD as front‐line regimen at Peking Union Medical College Hospital from January 1, 2013 to December 31, 2018. Results There were 107 patients with International Staging System (ISS) III and 51 with paraprotein of light chain. Of these, 77 completed nine cycles of the BCD regimen. As the number of treatment cycles increased, the proportions of serum and urine immunofixation electrophoresis (IFE) tests elevated from 40.39% to 62.22% and 16.75% to 37.78%, respectively. More than 90% of intact immunoglobulin chain MM patients were evaluated for blood M protein per cycle, but that of urinary M protein was less than 60%. The detection rate of urinary M protein in light chain MM was more than 70% per cycle. Patients with a very good partial response (VGPR) had longer progression‐free survival (PFS) than those with uncertain VGPR (32 vs. 26 months, p = 0.0336). Of the 141 patients who completed at least four cycles without undergoing autologous hematopoietic stem cell transplantation, those who were regularly assessed at every other cycle showed more favorable PFS than those who visited irregularly (27 vs. 22 months, p = 0.059). Conclusion Urinary M protein detection rate is significantly lower than that in serum, leading to an overestimation of efficacy, premature reduction of treatment intensity, and shortened PFS. Precise response assessments are critical to treatment decisions and clinical diagnoses.