Effect of MRD positivity on TTP HR over time. Flexible parametric survival models with time-varying effect modeled using the restricted cubic spline transformation of time at different time points: BM by (A) nested PCR and by (B) RQ-PCR; PB by (C) nested PCR and by (D) RQ-PCR. M, months after ASCT; R-CTX, rituximab-cyclophosphamide; R-HD-ARAC, rituximab-high dose cytarabine.