Prognostic value of stringent complete response (sCR) post-autologous stem cell transplant (SCT) in multiple myeloma (MM)
8587 Background: The measurement of serum immunoglobulin free light chains (FLC) has diagnostic and prognostic utility in MM. Normalization of the FLC ratio may define a deeper complete response after therapy than by standard criteria of CR. A sCR requires normalization of the FLC ratio and absence of clonal plasma cells in the bone marrow (BM) in addition to the standard criteria for CR. The objective of our study was to evaluate the impact of specific types of CR [sCR, CR or near CR (nCR/ immunofixation positive CR)] post-SCT on time to progression (TTP) and overall survival (OS). Methods: 468 MM patients who had achieved at least a partial response post-SCT were studied. The results of serum and urine protein studies, serum FLC assay, and BM evaluation, including measurement of marrow plasma cell clonality by immunohistochemistry obtained ≥60 days after SCT were used to determine the best response. TTP was defined as the time from SCT to progression, with non-myeloma related deaths censored. Results: 179 patients achieved varying degrees of CR as their best response. 39, 35 and 105 patients achieved nCR, CR and sCR, respectively. The median estimated follow-up for the entire cohort was 52 months from the diagnosis and 41 months from SCT. The median TTP was 15, 29 and 35 months for patients achieving nCR, CR and sCR, respectively (P<0.0001). The median OS for patients achieving nCR was 53 months from the diagnosis, but not reached for those with a CR or sCR (P=0.0009). The 5-year OS was 80% and 79% for patients with CR and sCR, respectively (P=NS). Similarly, OS from SCT was significantly shorter in patients achieving nCR (42 months vs. not reached for patients in CR and sCR; P<0.001). Conclusions: Achievement of a sCR represents a deeper response state compared to conventional CR, translating to a longer response duration post SCT, validating its inclusion in the modified uniform response criteria. While we did not see a significant improvement in OS with sCR compared to CR in this group, this question needs to be addressed in a larger study. The step wise improvement in the response duration across nCR, CR and sCR highlights the contribution of immunofixation studies, marrow assessment of clonality and FLC estimates. [Table: see text]