Study finds testicular cancer link for muscle-building supplements

Men who reported taking muscle-building supplements, such as pills and powders with creatine or androstenedione, reported a significantly higher likelihood of having developed testicular cancer than men who did not use such supplements, according to a new study in the British Journal of Cancer.

Moreover, said study senior author Tongzhang Zheng, the associated testicular germ cell cancer risk was especially high among men who started using supplements before age 25, those who used multiple supplements and those who used them for years.

"The observed relationship was strong," said Zheng, who led the study at Yale University before joining the Brown University School of Public Health as a professor of epidemiology. "If you used at earlier age, you had a higher risk. If you used them longer, you had a higher risk. If you used multiple types, you had a higher risk."

Testicular cancer incidence rose to 5.9 cases per 100,000 men in 2011, from 3.7 cases in 100,000 in 1975, Zheng said. Researchers aren't sure why.

"Testicular cancer is a very mysterious cancer," he said. "None of the factors we've suspected can explain the increase."

The study is the first analytical epidemiological study of the possible link between supplements and testicular cancer, the authors wrote in the journal. The work was inspired by mounting evidence that that at least some supplement ingredients may damage the testes.

The testicles are two small, egg-shaped glands located below the penis in the sac of loose skin called the scrotum. Testicles contain germ cells, which produce sperm, and other specialized cells that make the male hormone testosterone.

Testicular cancer is a relatively rare disease that is diagnosed in approximately 8,500 men in the United States each year. While it accounts for only 1 percent of all cancers in men, it is the most common solid tumor diagnosed in those aged 15 to 35.
Types of Testicular Cancer

The vast majority - about 95 percent - of testicular cancers begin in germ cells, specialized cells in the testicles that make sperm. While most germ cell tumors begin in the testicles, this type of tumor can occasionally arise in the abdomen, chest, or other areas of the body, even if there is no evidence of cancer in or near the testicles.

Two main types of germ cell tumors can develop in the testicles: seminoma and nonseminoma tumors. About half of all germ cell tumors are seminomas, which are usually slow growing. Many early-stage seminomas can be cured because this type of tumor does not usually metastasize, or spread, to other areas of the body. Nonseminomas are often more aggressive than seminomas, and are more likely to metastasize beyond the testicle.

About 5 percent of testicular cancers begin in stromal cells, which produce the hormone testosterone. Stromal cell testicular tumors are not typically cancerous. A tumor in the testicle could also be a "secondary" cancer, in which a cancer from another part of the body has spread to the testicle. One example is lymphoma, which usually begins in lymph nodes elsewhere in the body.