Associations between insulin-like growth factor 1, IGF-binding protein 3, and colorectal cancer.

[BACKGROUND] Higher serum insulin-like growth factor 1 (IGF-1) has been linked to colorectal cancer (CRC), with evidence supporting increased risk for colon but not rectal tumors. Few studies have included substantial numbers of non-Hispanic Black individuals, who have elevated population-level CRC risk. We investigated associations between IGF-1 and CRC in the Southern Community Cohort Study. We also report associations with IGF binding protein 3 (IGFBP-3), the primary IGF-1 transporter, and the IGF-1/IGFBP-3 ratio (a surrogate marker for biologically available IGF-1).

[METHODS] Participants with incident CRC (N = 297) were individually matched with controls (N = 604) on age, race, and sex. The majority of the cohort reports Black racial identity (75 %). Serum IGF-1 and IGFBP-3 were measured at enrollment. Logistic regression was used to estimate odds ratios (ORs) with 95 % confidence intervals (CIs) for CRC, colon and rectal cancers.

[RESULTS] For higher IGF-1 (tertile 3vs1), the OR for CRC was 1.45 (CI 0.95-2.21). Higher IGF-1 was associated with greater odds for colon cancer (OR 1.64, CI 1.01-2.64) but not rectal cancer (OR 0.93, CI 0.43-1.97). The associations with CRC and colon cancer were consistent among participants who fasted prior to serum draw (N = 356, CRC: OR 1.89, CI 0.95-3.78; colon cancer: OR 2.08, CI 0.96-4.51). No associations were observed for IGFBP-3 or the IGF-1/IGFBP-3 ratio in the full sample.

[CONCLUSION] Higher IGF-1 was associated with increased odds for colon cancer, but not rectal cancer, among predominantly non-Hispanic Black individuals with lower socioeconomic status, consistent with findings from predominantly non-Hispanic White cohorts.