PURPOSE: High levels of circulating tumor plasma cells (CTC-high) in patients with multiple myeloma are a marker of aggressive disease. We aimed to confirm the prognostic impact and identify a possible cutoff value of CTC-high for the prediction of progression-free survival (PFS) and overall survival (OS), in the context of concomitant risk features and minimal residual disease (MRD) achievement.METHODS: CTC were analyzed at diagnosis with two-tube single-platform flow cytometry (sensitivity 4 × 10^–5) in patients enrolled in the multicenter randomized FORTE clinical trial (ClinicalTrials.gov identifier: NCT02203643 ). MRD was assessed by second-generation multiparameter flow cytometry (sensitivity 10^–5). We tested different cutoff values in series of multivariate (MV) Cox proportional hazards regression analyses on PFS outcome and selected the value that maximized the Harrell's C-statistic. We analyzed the impact of CTC on PFS and OS in a MV analysis including baseline features and MRD negativity.RESULTS: CTC analysis was performed in 401 patients; the median follow-up was 50 months (interquartile range, 45-54 months). There was a modest correlation between the percentage of CTC and bone marrow plasma cells ( r = 0.38). We identified an optimal CTC cutoff of 0.07% (approximately 5 cells/µL, C-index 0.64). In MV analysis, CTC-high versus CTC-low patients had significantly shorter PFS (hazard ratio, 2.61; 95% CI, 1.49 to 2.97, P < .001; 4-year PFS 38% v 69%) and OS (hazard ratio, 2.61; 95% CI, 1.49 to 4.56; P < .001; 4-year OS 68% v 92%). The CTC levels, but not the bone marrow plasma cell levels, affected the outcome. The only factor that reduced the negative impact of CTC-high was the achievement of MRD negativity (interaction P = .039).CONCLUSION: In multiple myeloma, increasing levels of CTC above an optimal cutoff represent an easy-to-assess, robust, and independent high-risk factor. The achievement of MRD negativity is the most important factor that modulates their negative prognostic impact.

Mutations of the nucleophosmin gene (NPM1), in the absence of concurrent FLT3-internal tandem duplication (FLT3-ITD) have impressive prognostic value in patients with acute myelogenous leukemia (AML), carrying normal karyotype (NK). In this study we describe treatment results from a series of 19 patients with NPM+/FLT3- autografted in first complete remission (CR) after conditioning with a regimen, named BuI, based on high-dose continuous infusion of idarubicin and Busulfan. Ninety-nine consecutive patients (median age of 54 years) with NK AML autografted in first CR were analyzed. Nineteen of 99 patients (19%) had NPM1 mutation in the absence of FLT3 mutations. The control group, accounting for 80 patients, included 16 cases (15%) with both mutations, 10 (12%) with FLT3/ITD mutation and no NPM mutation, and 54 (68%) in whom neither NPM1 nor FLT3 mutations were detectable. The median overall survival (OS) for the whole patient population was 34 months, the median disease-free survival (DFS) was 22 months. Median OS and DFS were significantly longer for patients with isolated NPM1 mutation as opposed to controls (OS: not reached versus 25 months, P = .02; DFS: not reached versus 16 months, P = .007, respectively). Of interest, patients with isolated NPM1 mutation had a better outcome in terms of either OS or DFS compared to the group of 16 NMP1+/FLT3+ patients. In conclusion, our study suggest that BuI regimen results in favorable clinical outcome in patients with isolated NPM1 mutation, and could be investigated in a randomized study versus other regimes or repeated courses of high dose cytosine-arabinoside.