Prognostic Value of Refined Disease Risk Index (rDRI) and Conditioning Regimen in Adult Patients Receiving Unrelated Cord Blood Transplantation (UCBT) for Haematological Malignancies – 15-Year Follow-up of Multicenter Study in Singapore

Introduction:

Umbilical cord blood (UCB) is an established stem cell source for transplantation in patients with hematological diseases who lack suitable related or unrelated donors. Refined Disease Risk Index (rDRI) is a prognostic tool used in hematopoietic cell transplant (HCT), solely based on disease type and status. Its value in patients undergoing UCB transplants (UCBT) with different conditioning regime intensity is unclear. We sought to evaluate the predictive value of rDRI in patients undergoing UCBT.

Methods:

We performed a retrospective analysis of 107 adult patients with various hematological malignancies who underwent 4-6/6 HLA-matched UCBT using single unit UCB (n=14) or double unit UCB (n=93) between Aug 2006 and Nov 2019 at 2 academic tertiary hospitals in Singapore. Patients received pre-transplant conditioning with either myeloablative conditioning (MAC, n=63) regimen consisting of Fludarabine (Flu) 75mg/m2, Cyclophosphamide (Cy) 120mg/kg and total body irradiation (TBI) 12- 13.2Gy , intensified reduced intensity conditioning (i-RIC, N=22) regimen consisting of Flu 150 mg/m2, Cy 50mg/kg, thiotepa 10mg/kg and TBI 4 Gy, or nonmyeloablative conditioning (NM, n=22) regimen, consisting of Flu 200 mg/m2, Cy 50mg/kg and TBI 2 Gy. The median total nucleated cell dose infused was 5.07 x 10⁷/kg (range, 2.61 to 11.5)

Results:

Median follow-up was 84 months (range, 6 to 167 months).. Kaplan-Meier estimates of overall (OS) and event-free (EFS) survival at 10 years were 40 % (95% CI, 31-50) and 37% (95% CI, 28-47) respectively. At 2 years, cumulative incidence (CI) of relapse-related mortality (RRM) and non-relapse mortality (NRM) were 27% (95% CI, 18-35) and 35 % (95% CI, 25-45), respectively.

In multivariate analysis (MVA), rDRI showed significant correlation with OS (HR 2.41; 95% CI 1.41-4.11; p=0.001), EFS (HR 2.54; 95% CI 1.51-4.28; p=0.0004) and RRM (HR 2.71; 95% 1.36-5.41; p=0.005). Conditioning regimen intensity was found to have significant impact on NRM (p=0.047) and RRM (p=0.002) in MVA. When patients were further stratified into 4 risk groups incorporating both rDRI and conditioning regimen intensity, significant differences in OS (p=0.002) and EFS (p=0.001) were seen. 5-year OS (Figure 1) in patients receiving MAC/i-RIC and NM conditioning with low-intermediate risk rDRI were 52% and 36% respectively, compared with 24% and 13% in patients with high-very high risk rDRI (p=0.002). The corresponding ES were 50%, 29%, 20%, and 13%, respectively (Figure2).

Conclusions:

Our results confirm that rDRI has good predictive value for relapse and survival in UCBT recipients. Conditioning regime intensity was also found to have a significant impact on patient outcomes when evaluated together with rDRI. Prognostic scoring systems in HSCT are revised constantly with further studies needed to potentially incorporate the intensity of the conditioning regime into the rDRI. Outcomes in rDRI high risk patients remain poor and further studies are needed to define the best strategy that can induce sustained engraftment without increasing risk of relapse and toxicity death.