Prognostic impact of immunophenotypic complete response in patients with multiple myeloma achieving better than complete response.

To investigate the impact of immunophenotypic complete response [iCR, ≤10(-4) multiple myeloma (MM) cells defined by multicolor flow cytometry (MFC)] on survival in patients with MM, we retrospectively analyzed 78 patients that obtained conventional CR at our hospital. Survivals were landmarked at achievement of CR. The rate of stringent CR (sCR) among patients with CR was 88%, and iCR for CR and sCR patients were 44% and 49%, respectively. Achievement of iCR was associated with significantly longer disease-free survival (DFS) not only in CR patients (p = 0.009) but also in sCR patients (p = 0.002), while sCR attainment per se did not have statistically significant impact on DFS (p = 0.06) or overall survival (OS) (p = 0.587). Univariate and multivariate analyses indicated that attainment of iCR was independently associated with longer 2-year DFS in addition to creatinine (≤2.0 mg/dL) and maintenance therapy. This study highlights the importance of pursuing iCR even in patients with sCR.