Rob Delaporte was simply unlucky.
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He cannot blame a promiscuous lifestyle or misspent youth for his prostate cancer, though he wonders sometimes if his high protein diet had something to do with it.
It was his genes that did for him.
At age 44, when his father was diagnosed with prostate cancer, he decided to get himself tested and was surprised to learn that his PSA (prostate-specific antigen) levels were higher than normal.
To his further surprise, those levels were even higher a few months later. And to his shock, a biopsy revealed a moderately aggressive tumour in his prostate.
"When I got that diagnosis of cancer it was quite surreal," he said. "It was a huge shock."
Family history, age and African ancestry are the only established risk factors of prostate cancer among men.
But a growing body of evidence suggests there are some risk factors, such as obesity, that are within the power of individuals to control.
A study of 10,000 men that examined a wide range of potential determinants of prostate cancer has now identified a strong link between prostate cancer and sexual activity – with the risk of prostate cancer increasing with the number of sexual partners that a man has had.
The study, published in the International Journal of Cancer, found men who had more than seven sexual partners in their lifetime were twice as likely to have prostate cancer than those with fewer than three partners.
Men who had their first sexual experience before they were 17 and those who had more than five orgasms in the month prior to diagnosis also had higher odds of developing the disease, along with those who reached puberty earlier than their peers.
Cancer Council NSW research fellow Visalini Nair-Shalliker said sexual activity and metabolism were associated with antigen, a male sex hormone that is also strongly linked to the initiation of prostate cancer.
"The more partners you had, the more orgasms you had, the younger you were when you first had sex, all pointed to an increased prostate cancer risk," Dr Nair-Shalliker said.
It was important to identify risk factors so men could be given advice, and men aged over 50 who fell into those risk categories should speak to their doctors, especially if they had a family history of the disease, Dr Nair-Shalliker said.
It did not mean that having more sexual partners caused prostate cancer, merely that the two factors were associated.
"We can't make any recommendations around sexual activity because it's multi-faceted," Dr Nair-Shalliker said.
"We're not saying 'increase or decrease your sexual activity' because the evidence is still grey about that."
The findings on sexual activity are consistent with three other studies that found the risk of prostate cancer increased with sexual activity, but contrary to a 2014 Canadian study that found men who had more than 20 sexual partners in their lifetime had a 22 per cent lower risk of prostate cancer.
Mr Delaporte, who said he did not identify with any risk factors other than family history, had surgery to remove the tumour in March and was now "on the other side".
The experience prompted him to resign from his job with the border force and he is now studying to become a social worker.
