Radiation therapy may raise colorectal cancer risk among Hodgkin's lymphoma survivors

Individuals who received radiation therapy for Hodgkin's lymphoma (HL) are at increased risk of colorectal cancer, as reported in a study.

A nested case-control study was conducted to estimate the rate of colorectal cancer according to radiation dose to the large bowel and procarbazine dose among survivors of HL. Researchers reconstructed individual radiation therapy treatments on representative computed tomography data sets to estimate mean radiation doses to the large bowel.

A total of 316 participants (mean age at HL diagnosis 33.0 years, 69.9 percent men) with a history of HL were included in the study. Colorectal cancer occurred in 78 participants. They were matched according to age, age at HL diagnosis, and date of HL diagnosis to the 238 control participants without colorectal cancer.

The median interval between HL and colorectal cancer was 25.7 years. Colorectal cancer rates were higher among participants who received subdiaphragmatic radiation therapy for HL (rate ratio [RR], 2.4, 95 percent confidence interval [CI], 1.4–4.1) and those who received >8.4 g/m² procarbazine (RR, 2.5, 95 percent CI, 1.3–5.0).

A linear dose-response association was seen between colorectal cancer and radiation therapy, such that the incident rate increased commensurate with the mean radiation dose to the whole large bowel and the affected bowel segment.

Notably, procarbazine modified the association between radiation dose and colorectal cancer rate, with the association becoming stronger with increasing procarbazine dose. The excess rate ratio (ERR) to the whole bowel was 3.5 percent (95 percent CI, 0.4–12.6) per gray for patients who did not receive procarbazine. ERR increased by 1.2-fold (95 percent CI, 1.1–1.3) for every 1-g/m² increase in procarbazine dose.

The findings may aid in estimating individualized colorectal cancer risk, identifying high-risk survivors for subsequent screening, and optimizing treatment strategies.