A study published in the British Journal of Cancer suggests that tests to grade and stage prostate cancer underestimated the severity of the disease in half of men whose cancers had been classified as 'slow growing'.
Scientists from the University of Cambridge compared the staging and grading of cancer in over 800 men before and after they had surgery to remove their prostate. They found that of the 415 men whose prostate cancer was classified as slow growing and confined to just the prostate after an initial biopsy, half (209) had cancer which was more aggressive than originally thought when assessed again after surgery and almost a third (131) had cancer that had spread beyond the prostate.
Greg Shaw, a urological surgeon and one of the study authors based at the Cancer Research UK Cambridge Institute, said: "Our results show that the severity of up to half of men's prostate cancers may be underestimated when relying on tests before they have surgery.
"This highlights the urgent need for better tests to define how aggressive a prostate cancer is from the outset, building on diagnostic tests like MRI scans and new biopsy techniques which help to more accurately define the extent of the prostate cancer. This would then enable us to counsel patients with more certainty whether the prostate cancer identified is suitable for active surveillance or not.
"Whilst active surveillance would seem to be a safe approach for some men, nearly a third will end up needing surgery or radiotherapy within five years."
Prostate cancer is the most common cancer in men in the UK with around 41,700 new cases diagnosed every year. Last year there were around 10,800 deaths in the UK from prostate cancer. The severity of prostate cancers is assessed using biopsy, MRI and PSA tests.
Professor Malcolm Mason, Cancer Research UK's prostate cancer expert, said: "Despite the limitations that this study shows, all evidence so far points to active surveillance being safe provided men are carefully selected. But we need better methods of assigning a grade and stage so that no man has to unnecessarily undergo treatment, while at the same time making sure we detect and treat the cancers that really need it."
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Shaw, GL et al. "Identification of pathologically insignificant prostate cancer is not accurate in unscreened men." (2014) British Journal of Cancer