Is radiotherapy a safe option for men with prostate cancer? Sophie Lutter delves behind the headlines to see what the science says.

3 Mar 2016

Today, a research paper published in the British Medical Journal concluded that there was some association between radiotherapy to the prostate and risk of secondary cancers in the bladder, bowel and rectum. The story has been picked up and reported in the press. But does this mean that radiotherapy isn’t a safe option for men with prostate cancer?

No. But as usual, it’s a bit more complicated than that…

The researchers looked at a number of different studies that compared outcomes in men who had had radiotherapy, and men who hadn’t. Their overall comparisons revealed that men who had radiotherapy were 39 per cent more likely to also have bladder cancer, 68 per cent more likely to have colorectal cancer and 62 per cent more likely to have rectal cancer than men who hadn’t had radiotherapy. These are what’s known as ‘relative risks’ – the relative likelihood of something happening in one group that’s been treated one way compared to the likelihood of the same thing happening to another group that’s been treated a different way.

But although these numbers look pretty scary, they can actually also be quite misleading, because they don’t give any indication of what this means in real numbers.

So the researchers calculated this as well, but this hasn’t been picked up by the newspapers.

In real terms, there were between 0 and 0.6 more cases of bladder cancer, 0.2 and 1.4 more cases of colorectal cancer, and -0.2 and 1 more cases of rectal cancer per 100 men who’d had radiotherapy compared to men who hadn’t.

As you can see, these numbers are far less scary.

There are a few other interesting points which were identified by the researchers behind the study which might explain some of these differences: 

  • Patients treated with radiotherapy might experience side effects from their treatment such as increased bowel urgency, rectal bleeding and other  symptoms, and so there is chance that secondary colorectal and rectal cancers may be more regularly detected in these men, creating a selection bias.
  • The studies included in this analysis lacked important information on confounders, comorbidities and other risk factors associated with cancers other than prostate cancer, which might be higher in patients who are treated with radiotherapy.
  • As our very own Dr Matthew Hobbs says, there may be some variability between different types of radiotherapy and so “modern types of radiotherapy (brachytherapy for example) are likely to have a lower risk than the techniques analysed here.”

The researchers’ conclusions from this work were that these risks should be weighed in the balance when a man is deciding what type of treatment to have. This is especially true for men who can be expected to live for 20 years or so after their prostate cancer treatment, because the risk of developing another cancer does increase with time after treatment.

Men diagnosed with localised prostate cancer who are looking at their treatment options might want to take this into consideration when deciding between active surveillance, radiotherapy or surgery. However, based on this study, the increased risk of secondary cancer for men undergoing radiotherapy is slight.

For men who are at a higher risk of aggressive prostate cancer (Black men and men with a family history of prostate cancer), the benefits of treatment from radiotherapy far outweigh the small chance of a secondary cancer developing as a result of the treatment.

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