Testicular cancer has always been sort of an odd-ball in the world of cancer, particularly because it occurs disproportionately in younger men. The average occurrence for testicular cancer onset is around 30 years of age; 84 percent of all cases are aged 15-49 but just six percent occur in men over 60. To put that in perspective, a United Kingdom study found that more than a third of all cancers are in the elderly.
But a new study finds that the main cause of testicular cancer also contributes to its status as a unique cancer.
Researchers working in the U.S., U.K., Germany and Sweden used a two-pronged approach to investigate the degree to which testicular cancer was inherited. The first approach was using population analysis from the Swedish family-cancer database, where researchers had access to historical data from over 15 million cancer patients, 10,000 of whom had testicular cancer.
Their second approach was to analyze the genome of 6,000 men from the U.K., 1,000 of whom had testicular cancer. The results, published in the journal Scientific Reports, found that just under half (48.9 percent) of testicular cancers result from inheritance. Interestingly, the scientists found that the inherited cancer-causing genes were actually several small pieces of mutated DNA, rather than a specific gene (like the BRCA genes that are linked to breast and prostate cancer).
To get some perspective on just how high this percentage is, consider that experts estimate that, at most, 10 percent of breast, colorectal and pancreatic cancers are caused by genetic inheritance.
Scientists classify cancer causes in one of three ways: sporadic, hereditary and family cluster. The overwhelming majority, meaning 70 to 80 percent of cancers -- although some estimates are even higher -- are sporadic. What this means is that the cancer is brought on by DNA damage from the normal aging process, or environmental factors (i.e. smoking, which causes about 90 percent of lung cancers, and HPV, which causes over 99 percent of cervical cancers).
As for the hereditary group, they make up just 5-10 percent of all cancer origins. Meanwhile, familial clusters, cancers that arise due to inheriting genetic susceptibilities but those of which that also have strong sporadic factors, make up as much as 20 percent.
Credit: North Shore LIJ Staten Island University Hospital
The unexpectedly high contribution of inheritance of testicular cancer shines light on just how little we know about the causes of cancer, despite what we may hear in the media. The study's authors explain that when it comes to testicular cancer research, there's been a long-held belief that some unique, environmental factor is responsible for doubling the incidence of testicular cancers in Europe over the past 40 years. These data poke a large hole in that theory.