ASCO GU 2018: Diagnostic Radiation and Testicular Germ Cell Tumor Risk

San Francisco, CA ( Dr. Kevin Nead and colleagues presented their work assessing diagnostic radiation and testicular germ cell tumor risk. Dr. Nead notes that both the incidence of testicular germ cell tumors (TGCT) and use of diagnostic radiation have increased in recent decades. In a quarter of diagnostic scans in children, direct and indirect radiation dose to the testes exceeds 20 mSv, which surpasses thresholds associated with malignancy risk (~5 mSv). The objective of this study was to examine the association between exposure to diagnostic radiation and TGCT risk in a case-control study. 

For this study, cases were enrolled in a hybrid hospital- and population-based setting and controls were recruited from the community. Participants reported on exposures to x-ray/CT below the waist and lower GI series, and subsequently the authors derived a combined variable for any exposure. After imputation to infer missing data, baseline characteristics were compared and multivariable logistic regression models adjusting for age and race were used to determine the risk of developing TGCT according to number of exposures and age at first exposure.

Cases (n = 1088) were more likely than controls (n = 1458) to be white, have a family history of TGCT, and have a history of cryptorchidism (p < 0.05). There was an increased risk of TGCT with a greater number of exposures for both x-ray/CT (ptrend= 0.002) and the combined diagnostic radiation variable (ptrend< 0.001). Compared to those without any exposure, risk was greatest among those reporting ≥6 exposures for x-ray or CT (OR 9.6, 95%CI, 4.6-19.9) and the combined variable (OR 5.8, 95%CI, 3.2-10.4), after adjusting for age at first exposure. Early first exposure before eleven years of age increased risk of TGCT for x-ray/CT (OR 2.36, 95%CI, 1.17-4.77) and combined radiation exposure (OR 1.96,95%CI, 1.05-3.67) compared to later first exposure after seventeen years of age, adjusting for total exposures. Analyses limited to observed data only yielded similar results.

The authors concluded that exposure to diagnostic radiation below the waist, particularly among younger individuals, may increase TGCT risk. As the testes are present outside the body and rarely examined using diagnostic radiation, a unique opportunity for shielding exists. Efforts to reduce testicular dose and optimize shielding practices should be prioritized. These results should be validated with additional studies.

Presented by:  Kevin Nead, MD, MPhil University of Pennsylvania Perelman School of Medicine Hospital, Philadelphia, PA

Co-Authors: Nandita Mitra, Benita Weathers, Louisa T Pyle, Katherine L. Nathanson, Peter A Kanetsky; University of Pennsylvania Perelman School of Medicine Hospital, Philadelphia, PA; University of Pennsylvania Perelman School of Medicine, Philadelphia, PA; University of Pennsylvania, Philadelphia, PA; Moffitt Cancer Center Cancer Epidemiology Program, Tampa, FL

Written by: Zachary Klaassen, MD, Urologic Oncology Fellow, University of Toronto, Princess Margaret Cancer Centre, @zklaassen_md at the 2018 American Society of Clinical Oncology Genitourinary (ASCO GU) Cancers Symposium, February 8-10, 2018 - San Francisco, CA