medwireNews: Patients who receive carbon ion radiotherapy for localized prostate cancer have a significantly lower risk for subsequent primary cancers than those treated with photon radiotherapy or surgery, retrospective study data suggest.
“Although prospective evaluation with longer follow-up is warranted to support these results, our data supports a wider adoption of carbon ion radiotherapy for patients with expected long-term overall survival or those with poor outcomes after receiving conventional treatments,” write Hirokazu Makishima (National Institute of Radiological Sciences [NIRS], Chiba, Japan) and co-authors in The Lancet Oncology.
During a median 7.9 years of follow-up, 15% of 1455 patients who received carbon ion radiotherapy for prostate cancer at NIRS between 1995 and 2012 developed at least one subsequent primary cancer, most commonly in the stomach (19%), lung (17%), colon (12%), or bladder (9%).
The risk for subsequent cancer was significantly higher among patients aged 71 years and older compared with those aged 60 years and younger, and among smokers.
When Makishima and team compared the NIRS patients with prostate cancer with patients from the Osaka registry who were treated with photon radiotherapy (n=1983) or surgery (n=5948), they found that the cumulative incidence of subsequent primary cancers at 9.9 years was lower with carbon ion radiotherapy than with either the photon radiotherapy or surgery, at 16.1% versus 24.0% and 18.7%, respectively.
Furthermore, pairwise comparisons using propensity score-weighted analyses showed that carbon ion radiotherapy was associated with a significant 20% lower risk for subsequent primary cancers than photon radiotherapy and a significant 19% lower risk than surgery. By contrast, photon radiotherapy was associated with a significant 18% higher risk for subsequent primary cancers than surgery.
The researchers note that the lower risk in the carbon ion radiotherapy group appeared to be driven by a lower risk for colon and rectum cancers, but they also point out that all of the second primary cancers they included “could be either spontaneous or radiation-induced cancers because the cause of these malignancies was impossible to ascertain from the epidemiological data available.”
The team acknowledges study limitations such as the relatively short follow-up, missing data on potential confounders such as alcohol or tobacco use and comorbidities, and limited details on radiotherapy dose, volume, and radiation technique.
Nevertheless, they conclude that the “results from this hypothesis-generating study should encourage further research on subsequent malignancies and suggest that carbon ion radiotherapy might have an important role in treating patients with prolonged life expectancies.”
In an accompanying commentary, Charles Catton and David Shultz, both from the University of Toronto in Ontario, Canada, say that the data show that although carbon ion radiotherapy appears to reduce this risk for second primary cancers relative to photon radiotherapy, “limited access to [carbo ion radiotherapy] facilities makes it impractical for most patients.”
Furthermore, they caution that the study “should not encourage a general move from photon radiotherapy for those who choose radiotherapy for their prostate cancer. Ready access, favourable economics, and abundant level 1 evidence of safety and efficacy weigh heavily in its favour.”
Nonetheless, Catton and Shultz conclude that “the risk of radiation-related second malignant neoplasia should be a part of patient discussion, especially for younger patients with treatment options beyond photon radiotherapy.”
By Laura Cowen
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