Abstract 4636: Inverse association of eosinophil count with colorectal cancer incidence in the Atherosclerosis Risk in Communities study

Background: A theory of immunosurveillance suggests that allergic conditions could reduce cancer risk by enhancing the ability of the immune system to detect and remove malignant cells. A history of allergy has been associated with reduced risk of several malignancies, including pancreas, mouth, throat, colorectum, and skin. We hypothesized that blood eosinophil count, a marker for allergic disorders, is inversely associated with the risk of colorectal cancer (CRC) in the Atherosclerosis Risk in Communities (ARIC) prospective cohort. To our knowledge, the association between blood eosinophil count and cancer risk has not been investigated before. Methods: Relative eosinophil and total leukocyte counts – were measured in blood at baseline (1987-89) and at visit 2 (1990-92). Absolute eosinophil counts were calculated by multiplying relative count by the total leukocyte count at each visit. Proportional hazard regression models were used to estimate the hazard ratios (HR) and (95% confidence interval, CI) of CRC in relation to absolute eosinophil count after adjustment for age, race, sex, center, education, body-mass index, smoking status, pack-years of smoking, alcohol drinking status, diabetes, leukocyte count, and fibrinogen. Results: At baseline, the mean age of this analytical cohort was 53.9 years, 26% were African American, 74% were Caucasians, and 55% were women. During 177,386 person-years of follow-up (mean follow-up, 16.4 years) from 1987 through 2006, there were 242 incident CRC cases (187 colon and 56 rectal) in 10,804 participants, who were cancer-free at baseline. Compared to the lowest tertile of absolute eosinophil count at baseline, there was a statistically significant inverse association between eosinophil count and CRC incidence: HR =0.71 (95%CI, 0.51;0.98) for the second and HR=0.58 (95%CI, 0.41; 0.84) for the highest tertile (p-trend across tertiles was 0.004). A similar inverse association was observed for colon cancer, but there was no association with rectal cancer. The inverse association was consistent across the four ARIC centers, and there was no effect modification by age, sex, race, or smoking status. To exclude the potential effect of preclinical CRC on the eosinophil count, sensitivity analyses were performed after we excluded those CRC cases that occurred within five or ten years of follow-up, but all the associations remained. We repeated analyses in the subset of 6,854 initially cancer-free participants who also had an eosinophil count measured at visit 2 and observed a similar inverse association between absolute eosinophil count and the CRC risk. Conclusion: We observed an inverse association between blood eosinophil count and CRC risk. Since allergy is the most common cause for an increased eosinophil count in the developed world, these findings may reflect an inverse association of allergy with incident CRC. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4636. doi:10.1158/1538-7445.AM2011-4636