Abstract LB-360: Association between weight change after colorectal cancer diagnosis and long-term mortality differs by age
Authors: Kocarnik Jonathan M. , Hua Xinwei , Robinson Jamaica , Phipps Amanda I. , Cohen Stacey , Newcomb Polly A. 
Published: July 2016

Abstract
Previous studies evaluating the association of weight gain following colorectal cancer (CRC) diagnosis with mortality have been inconsistent. In this study, we evaluate whether this association differs by age at diagnosis.
Incident, invasive CRC cases were identified from the Puget Sound Surveillance, Epidemiology and End Results (SEER) Registry from 1997-2008 and enrolled in the Seattle Colon Cancer Family Registry. A standardized interview (at mean 8 months after diagnosis) ascertained self-reported height and weight two years prior. A follow-up questionnaire was administered approximately 5 years after baseline, with 1,087 participants providing height and weight at both time points. Survival outcomes were assessed through linkage to the National Death Index. Delayed-entry Cox regression was used to estimate the association between change in weight (kg) and all-cause or CRC-specific mortality (Hazard Ratio (HR) and 95% Confidence Interval (95% CI)), with survival time beginning at the 5-year follow-up survey. Models adjusted for age at diagnosis, sex, smoking history (ever/never), cancer stage at diagnosis (I-IV, missing), days from diagnosis and baseline survey, and body mass index (kg/m2) at baseline. Analyses were stratified by age at diagnosis (&lt;50 or ?50 years). We also evaluated an interaction term between age at diagnosis (continuous) and per-kg weight change.
Over a median 4.7 years (range 0-9.0) of follow-up after the 5-year survey, 234 participants died (69 from CRC). At the 5-year follow-up, 579 (54%) participants had lost weight (median -5 kg), 114 (11%) reported the same weight, and 385 (36%) had gained weight (median 4 kg).
Among those aged &lt;50 at CRC diagnosis, weight gain at follow-up was significantly associated with higher subsequent all-cause mortality (HR = 1.19 per 5kg, 95% CI: 1.02-1.39), but not CRC-specific mortality. Among those aged ?50 at CRC diagnosis, weight gain at the follow-up time point was significantly associated with higher CRC-specific mortality (HR = 1.34 per 5kg, 95% CI: 1.11-1.61), but not all-cause. The association between weight change and survival differed by age for CRC-specific mortality (P-interaction = 0.01) but not all-cause mortality (P-interaction = 0.82). These findings support the importance of maintaining a healthy body weight after CRC diagnosis, and may suggest the association of weight change with risk of cause-specific death differs in individuals younger versus older than age 50 at diagnosis.
Citation Format: Jonathan M. Kocarnik, Xinwei Hua, Jamaica Robinson, Amanda I. Phipps, Stacey Cohen, Polly A. Newcomb. Association between weight change after colorectal cancer diagnosis and long-term mortality differs by age. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-360.