Conditional Survival and Cause-Specific Mortality in Patients Undergoing Allogeneic Hematopoietic Cell Transplantation (alloHCT) for Hematologic Malignancy Over Three Decades
Authors: Armenian Saro H. , Sun Can-Lan , Vase Tabitha , Mills George , Atencio Liezl , Francisco Liton , Palmer Jocelynne , VanderWalde Ari , Wong F. Lennie , Rosenthal Joseph , Kogut Neil Martin , Popplewell Leslie , Snyder David S. , Stein Anthony Selwyn , O'Donnell Margret , Forman Stephen J. , Bhatia Smita 
Published: October 2019

Abstract
Abstract 606

Background:
alloHCT is offered with curative intent to patients with hematologic malignancies, and conventionally-computed survival estimates are offered for prognosticating outcomes. However, conventionally-computed survival estimates do not take into account elapsed time (and changing hazards with time survived); conditional survival overcomes these limitations, by calculating the probability of survival after having already survived a certain period of time – such data are unavailable for alloHCT recipients. We describe cause-specific (relapse-, GvHD-, treatment-related) conditional survival after alloHCT, providing clinically relevant information for patients who have survived 6 mos, 1, 2, and 5y after alloHCT.

Methods:
From 1976 to 2006, 2,427 consecutive patients received alloHCT for a hematologic malignancy at a single institution (median age: 34.7y [0.6–72.5]). Vital status and cause of death were determined using National Death Index, Social Security Death Index and medical records.

Results:
As of 12/31/2007, a total of 1413 deaths (58% of the cohort) were observed; 39% attributed to recurrent disease; 34% to GvHD; 12% to infection; 5% to cardiopulmonary disease; 2% to subsequent malignant neoplasm (SMNs); and 8% to other causes. Conventionally-computed probability of survival was 44.6% at 5y and 41.2% at 10y from alloHCT. On the other hand, conditional on survival for 6 mo, 1, 2, and 5y after alloHCT, 5-y survival rates were 62%, 75%, 83%, and 93%, respectively (Figure A). The cohort was at a 40-fold increased risk of any death compared with the general population (95%CI=38.2–42.4); at a 25.6-fold increased risk of death due to pulmonary complications, 3.3-fold risk due to SMNs, and 2.3-fold risk due to cardiovascular complications. Among patients followed for 15+y after HCT, the risk of all-cause mortality was 2.6-fold that of the general population (95%CI=1.8–3.7). Standardized mortality ratios (SMR) and cause-specific conditional mortality rates by primary diagnosis are summarized in the Table.
Individuals who survived the first 5y had negligible (≤5%) risk of relapse- and GvHD-related mortality over the subsequent 5y. Treatment-related mortality increased over time; among those who survived 5y, treatment-related mortality rates exceeded relapse-related mortality (Figure B). After adjustment for demographics, underlying diagnosis and treatment era, individuals with chronic GVHD (cGVHD) had a significantly lower risk of relapse-related mortality (RR=0.43, 95%CI=0.4–0.5) compared to those without cGVHD.

Conclusions:
The projected 5-y survival rates improve conditional on time survived from alloHCT; 5-y survival exceeds 93% for those who have already survived 5y. However, alloHCT recipients who have survived 15+y continue to remain at increased risk of death compared to the general population. cGVHD is associated with decreased risk of relapse-related mortality. Both relapse-related and GvHD-related mortality rates decline with time, such that, among those who have survived 5y, treatment-related mortality exceeds relapse-related mortality. Conditional survival estimates provide clinically relevant prognostic information, helping inform preventive and interventional strategies.

Disclosures:
No relevant conflicts of interest to declare.