Differential effects of patient-related factors on the outcome of radiation therapy for rectal cancer.

Abstract

The objective of this study was to investigate whether cancer specific survival in rectal cancer patients is affected by patient-related factors, conditional on radiation treatment. 359 invasive rectal cancer patients who consented and provided questionnaire data for a population-based case-control study of colorectal cancer in Metropolitan Detroit were included in this study. Their vital status was ascertained through to the population-based cancer registry. Hazard ratios (HR) for cancer specific and other deaths and 95% confidence intervals (CIs) were calculated according to selected patients' characteristics, stratified by radiation status, using joint Cox proportional hazards models. A total of 159 patients were found to be deceased after the median follow-up of 9.2 years, and 70% of them were considered to be cancer specific. Smoking and a history of diabetes were associated with an increased probability of deaths from other causes (HR 3.20, 95% CI 1.72-5.97 and HR 2.02, 95% CI 0.98-4.16, respectively), while regular use of non-steroidal anti-inflammatory drugs (NSAIDs) was inversely correlated with cancer-specific mortality (HR 0.50, 95% CI 0.30-0.81). Furthermore, the associations of smoking and NSAIDs with the two different types of deaths (cancer vs others) significantly varied with radiation status (P-values for the interactions= 0.014 for both). In addition, we observed a marginally significantly reduced risk of cancer specific deaths in the patients who had the relative ketogenic diet overall (HR=0.49, 95% 0.23-1.02). Further research is warranted to confirm these results in order to develop new interventions to improve outcome from radiation treatment.