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

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. Three hundred fifty-nine 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 (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.