Between 2001 and 2016 in the United States, Asian/Pacific Islander men experienced the greatest increase in the incidence of testicular germ cell tumors, followed by Hispanic and American Indian/Alaska Native men, according to a study published by Ghazarian et al in Cancer Epidemiology, Biomarkers & Prevention.

Testicular germ cell tumor is the predominant form of testicular cancer, which is the most frequently occurring cancer among men between the ages of 15 and 44 years in the United States. The incidence of testicular germ cell tumor has been increasing since the mid-20th century, but the underlying reasons for the increase remain unclear.

“While risk factors are not well understood, testicular germ cell tumor is known to be associated with other male reproductive disorders. As such, increases in incidence can be indicative of problems in male reproductive health,” explained Armen Ghazarian, PhD, MPH, first author of the study and a program director in the Division of Cancer Control and Population Sciences at the National Cancer Institute (NCI) at the National Institutes of Health.

Testicular germ cell tumor is most common among men of Northern European ancestry; however, a previous study published by Dr. Ghazarian and colleagues in the journal Cancer revealed that rates increased among Hispanic men between 1998 and 2011. “We have long known of the risk among men of Northern European ancestry, but the results of our previous study highlighted that rates were increasing among other racial/ethnic groups as well,” said Dr. Ghazarian. The latest study builds on this work.

“We expanded our analysis to include data from across the U.S.,” noted Katherine McGlynn, PhD, MPH, senior author of the study and a senior investigator in the Division of Cancer Epidemiology and Genetics at NCI. “The goal was to determine if similar trends persisted in the more recent data. Monitoring trends is critical to building a better understanding of potential risk factors.”

Analysis Results

In this study, Drs. Ghazarian and McGlynn examined testicular germ cell tumor incidence data from the U.S. Cancer Statistics public use databases. The analysis included data on testicular germ cell tumor cases reported between 2001 and 2016 from registries in all 50 states and the District of Columbia.

The authors found that the incidence of testicular germ cell tumor was highest among non-Hispanic white men, followed by Hispanic, American Indian/Alaska Native, Asian/Pacific Islander, and non-Hispanic black men.

While the incidence of testicular germ cell tumor increased across all racial/ethnic groups during this period, the authors found that Asian/Pacific Islander men experienced the greatest increase, with an annual percent change (APC) of 2.47. All other racial/ethnic groups experienced annual rate increases as well: Hispanic men (APC = 2.10), American Indian/Alaska Native men (APC = 1.71), non-Hispanic black men (APC = 1.28), and non-Hispanic white men (APC = 0.41).

Geographic Differences

The authors also examined differences in testicular germ cell tumor incidence by geographic region as defined by the U.S. Census Bureau. They found that Asian/Pacific Islander, Hispanic, and American Indian/American Native men had the highest incidence of testicular germ cell tumor in the West, while non-Hispanic black and non-Hispanic white men had the highest incidence in the Northeast.

Although significant increases in incidence among Hispanic men were observed in all geographic regions, significant increases in incidence were observed for Asian/Pacific Islander men in the West, non-Hispanic black men in the South, and non-Hispanic white men in the Northeast and Midwest. However, Dr. Ghazarian cautioned that these results may partially reflect the distribution of different racial/ethnic groups across the country.

A previous study published by Gurney et al in European Urology examining global trends did not find similar increases in testicular germ cell tumor incidence in Asian countries. “Given the differences in trends, it would be interesting to examine U.S. trends using data on the birthplace of Asian/Pacific Islander men, as there could be an interplay between genetic and environmental risk factors,” noted Dr. McGlynn. In her ongoing work, she aims to understand the contribution of environmental exposures, such as endocrine-disrupting chemicals, on testicular germ cell tumor risk.

“I hope the results from this study will increase awareness of testicular germ cell tumor among men of all racial/ethnic groups,” said Dr. McGlynn. “While incidence remains highest among non-Hispanic white men, it is becoming increasingly clear that this disease does not just affect men of European ancestry.”

A limitation of the study was that all Asian/Pacific Islander men were examined as a single group, rather than by individual ancestry. This was also the case for Hispanic men. These groupings prevented the examination of whether risk was specific to men of certain ancestries. Another limitation was the lack of data regarding birthplace; incidence trends could be different for men who emigrated to the United States compared to men of the same racial/ethnic group who were born in the United States.

Disclosure: The study was supported by the National Cancer Institute. For full disclosures of the study authors, visit cebp.aacrjournals.org.