A recent meta-analysis published in The BMJ finds a link between radiotherapy for prostate cancer and an increased risk of secondary cancers. The authors discuss the implications for clinicians and patients.
Individuals diagnosed with prostate cancer have two main treatment options: surgery or radiotherapy.
Another potential, but as yet unproven, side effect of radiotherapy with prostate cancer is the generation of a second primary cancer (second malignancy).
This connection has been investigated in numerous studies, but a definitive answer has not been forthcoming.
Radiation is known to cause second malignancies in patients with Hodgkin’s lymphoma and some other cancers, but research into prostate cancer treatment has not yielded such clear-cut results.
There is some evidence that radiation treatment on the prostate produces radiation scatter further afield, causing genetic mutations elsewhere in the body. This so-called bystander effect is not fully understood, but it seems that radiotherapy induces the release of extracellular factors which, in turn, generate mutations in cells well away from the firing line.
A team of researchers, led by Dr. Robert Nam, at the University of Toronto, Canada, decided to reopen lines of investigation and carried out a meta-analysis of 21 studies. They compared rates of second malignancies in prostate cancer patients who had undergone radiotherapy with those who had not.
The team found that the patients who had opted for radiotherapy had a higher incidence of bladder, colorectal and rectal cancer. However, cancers of the blood and lungs did not increase.
These results remained significant, even after the researchers restricted the analysis for follow-ups to 5 and 10 years after radiotherapy.
The authors are quick to note that the elevation in risk is minimal. For instance, the largest absolute risk was for colorectal cancer with a 0.3-4.2% increase.
A study of this type cannot prove cause and effect, so more work will need to be done to confirm the results. Dr. Nam believes these findings are worth considering for patients who have a life expectancy of 20 years or more. He says:
“This information could be particularly important to a large proportion of patients where treatment is recommended and, according to treatment guidelines, where surgery or radiation would be equal options for them to choose.”
The meta-analysis is accompanied by an editorial written by Christine E. Eyler, clinical fellow, and Anthony L. Zietman, professor of radiation oncology, both from Massachusetts General Hospital. The piece, entitled “A (relatively) risky business: the link between prostatic radiotherapy and second malignancies,” discusses the findings and how they might impact clinician and patient decisions.
The authors note that, although secondary malignancies might be more common in radiation-treated patients as compared with surgical patients, mortality is not necessarily altered, especially with smaller cancers picked up during treatment for other issues. They say:
“Indeed, there seems to be no survival difference between men with bladder cancers linked to previous prostate irradiation and bladder cancers identified in patients treated with surgery.”
Ultimately, the risk factors have to be weighed up for each individual patient. The editorial’s authors go on to say “clinicians and patients must decide together whether, for example, the roughly 1.4-1.7-fold increase in relative risk of a second malignancy after a 10-year lag period justifies alternative treatments.”
According to the editorial, the findings confirm a hunch that doctors have had for many years. Further investigation is predicted to firm up the findings. In other cancer-related news, Medical News Today recently covered research asking whether herbal remedies might be dangerous for cancer patients.