Ben Stiller's declaration that a prostate cancer test saved his life is under scrutiny from doctors.

The comedic actor and director revealed this week that he was diagnosed with prostate cancer two years ago when he was 48.

In an essay posted on the website Medium, Stiller recounted his experience, including his lack of a family history, high-risk status or symptoms, the "crazy roller coaster ride" of diagnosis to the first cancer-free test result three months later and drawing strength and anxiety of searching for men who had prostate cancer" and "people who died of prostate cancer" on Google.

"Taking the PSA test saved my life. Literally. That's why I am writing this now," Stiller wrote.

The prostate specific antigen or PSA test is a measure of inflammation, which can be elevated for reasons besides cancer.

In Stiller's case, his PSA levels rose for more than a year and a half before his urologist performed a physical exam, suggested an MRI and then a biopsy that came back positive. His Gleason score, which his based on how the cancer cells appear under a microscope, of 7 was categorized as "mid-range aggressive cancer."

He was treated with a robotic assisted laparoscopic radical prostatectomy

But whether the test saved Stiller's life is unclear, said Dr. Neil Fleshner, a professor and chair of urology at the University of Toronto.

The actor's treatment plan was looking for a 35 to 40-year-old solution, something difficult to foresee.

"Nobody knows the 40-year natural history of prostate cancer, and that's that dilemma men always face. We know statistically it might not harm you for 10 or 15 years but they do grow," Fleshner said.

Slow-growing versus aggressive cancers

About 4 per cent of men are destined to die of prostate cancer, Fleshner noted.

In most men with prostate cancer, the tumour grows slowly, and they're likely to die of another cause before the prostate tumour causes any symptoms.

The challenge for doctors and specialists is distinguishing the majority of slow-growing prostate cancers that won't cause harm from more aggressive ones like Stiller's. Harms from overtreatment, including biopsies, can result when harmless tumours are treated.

Fleshner views illness in male celebrities such as Stiller as an opportunity to encourage men to visit a doctor.

"Many men, once their mommies stop taking them to the doctor, rarely go see a doctor again until they're well into their 40s. A lot of diseases get missed. High blood pressure, opportunities to intervene around sedentary lifestyle," Fleshner said. "A lot of preventative health practices should be taking place earlier than that."

A commentary by Kevin Lomangino, an editor at HealthNewsReview, which questions health news, said celebrities have a responsibility to use their platform wisely.

Sadly, it's possible Stiller's case is an aggressive one that will recur despite the early detection and treatment, meaning his declaration of having his "saved" will turn out to be premature, Lomangino wrote.

It is a possibility, Fleshner acknowledged, but believing in treatment when it's embarked on is an important part of rehabilitation, he said.

The Canadian Cancer Society estimates that in 2015, 24,000 men will be diagnosed with prostate cancer. And 4,100 men will die from it, which represents 10 per cent of cancer deaths in men.