DIAGNOSTIC TESTS AND RISK OF TESTICULAR CANCER

 Over the last 40 years, there has been a doubling in the incidence of testicular cancer. Over the same period, there has been a 20-fold increase in the use of diagnostic radiation, and the doses of radiation used have increased sevenfold. Perhaps the two are related?

The suggestion comes from researchers reporting a new case-control study in which they show that repeated diagnostic radiation below the waist was associated with an increase the risk of testicular germ cell tumor (TGCT).

The study involved 315 men with TGCT and 931 controls from hospital and population-based settings, and analyzed medical records and individuals'  recall of diagnostic radiation such as CT scans, x-rays, and barium enema.

Compared with men who did not undergo any diagnostic radiation, the risk of testicular cancer was nearly twofold higher among men who had undergone three or more diagnostic X-rays and CT scans, and more than fourfold higher among men who had undergone three or more lower gastrointestinal (GI) series or barium enema.

The study was published online November 11 in PLoS ONE.

Testicular cancer, the most common cancer in white men aged 15-44, has steadily increased in incidence in the United States over the past three or four decades: the rate has jumped from 3 out 100,000 men in 1975 to 6 out of 100,000 men today, say senior author Katherine Nathanson, MD, of the University of Pennsylvania in Philadelphia, and colleagues.

"Our data suggests that the increased use of diagnostic radiation below the waist in men over that same time may contribute to the increase in incidence," Nathanson said in a press statement.

Reducing diagnostic radiation doses to the testes "should be prioritized," say the investigators, if these results are validated by additional research.

It's "undoubtedly prudent" to reduce those doses "as much as possible," said David Brenner, PhD, director, Center for Radiological Research, Columbia University Medical Center, New York City, who was asked for comment.

I do find the results quite surprising. Dr David Brenner

However, Brenner also had reservations about the new study. "I do find the results quite surprising," given what is known historically about testicular cancer and radiation exposure, he said.

Higher radiation doses (than in the current study) in two other settings (among post-atomic bomb survivors and in the treatment of ankylosing spondylitis) are not associated with an increased risk of testicular cancer, he told Medscape Medical News in an email.

"Underlying conditions for which the individual received radiation imaging," may be one potential explanation for the increased testicular cancer risk seen in this study, he added.

Nathanson responded to Brenner's critique by focusing on atomic bomb survivors and pointing out that the baseline rate of testicular cancer in Asia, including Japan, is "very, very low" and therefore that population, including bomb survivors, is not a highly applicable comparison.

Take-Home Message: Testicular Shielding

Nathanson noted that diagnostic imaging below the waist is most commonly administered as a result of GI tract complaints such as constipation and abdominal pain.

For clinicians, the study's take-home message supports testicular shielding, she told Medscape Medical News.

Testicular shielding during diagnostic imaging can be protective, but audits show that correct use and positioning occurs in just 25% of pediatric diagnostic scans, the authors comment.

Recent epidemiologic studies support a tie between diagnostic radiation and other cancers, the authors also point out.

For example, women undergoing frequent x-rays for scoliosis may have an increased risk of breast cancer, and likewise for individuals undergoing repeat routine dental x-rays and thyroid cancer. Additionally, a National Health Service study among 175,000 children revealed an excess risk of subsequent brain tumors and leukemia tied to CT scans, say Nathanson and coauthors.

Total-dose and number of exposures were associated with an increasing cancer risk in each of the aforementioned studies.

Nathanson pointed out that Penn researchers have collected testicular cancer data since 2001 for the sake of research on related, inherited risk. The new study is an outgrowth of those efforts and is a rare effort in this subject area, in part, because testicular cancer is a very treatable rare cancer, with a 95% survival rate at 5 years.

A larger prospective study of the association between diagnostic radiation and testicular cancer would be better for determining causality, but is impractical given the needed time and associated costs. "A case-control design is a methodology that is ideally suited for studies investigating rare disease outcomes such as TGCT," the authors comment.

The study was supported with grants from the National Cancer Institute and the National Institutes of Health. The study authors and Brenner have disclosed no relevant financial relationships.