Flow MRD pre-blinatumomab consolidation, despite subsequent clearance, is associated with inferior survival in Ph+ B-ALL

Although adults with Philadelphia chromosome-positive (Ph+) B-cell acute lymphoblastic leukemia (B-ALL) may achieve a measurable residual disease-negative (MRD-) complete response (CR) after frontline treatment and blinatumomab (blina) consolidation, survival outcomes are heterogeneous, and known prognostic factors are limited. We conducted a retrospective, multicenter study of 81 adults with Ph+ B-ALL in MRD- (<10-4) CR1 after blina consolidation and stratified them by pre-blina MRD status as determined by multiparametric flow cytometry (flow). Patients who were pre-blina flow MRD- (n = 56) and flow MRD+ (n = 25) had similar baseline characteristics. With a median follow-up of 31.0 months, pre-blina flow MRD- patients had superior disease-free (DFS) and overall survival (OS) on univariate (p = 0.049 and p = 0.045, respectively) and multivariable analyses (HR 0.27, 95% CI 0.08-0.87 and HR 0.17, 95% CI 0.03-0.90, respectively) relative to pre-blina flow MRD+ patients. Inferior DFS was seen with the IKZF1-plus genotype (HR 3.51, 95% CI 1.08-11.44) and extramedullary disease at diagnosis (HR 3.90, 95% CI 1.19-12.73). In exploratory analyses, pre-blina flow MRD+ status remained associated with inferior DFS (p = 0.0005) and OS (p < 0.0001) for patients who did not receive a subsequent hematopoietic cell transplant (HCT) in CR1, but not in patients who did (p = 0.55 and p = 0.99, respectively). In summary, flow MRD+ status before blina consolidation was associated with inferior survival in patients with Ph+ B-ALL in CR1 despite subsequent clearance, and consolidative HCT may reduce this prognostic effect.