By Will Boggs MD
NEW YORK (Reuters Health) - 12/4/2019
The risk of subsequent primary cancer is lower after carbon-ion radiotherapy than after photon radiotherapy for localized prostate cancer, researchers from Japan report.
"In the setting of improving diagnostic and therapeutic interventions for prostate cancer, subsequent primary cancer will become an important issue to consider as patients are expected to live longer," said Dr. Hirokazu Makishima of the National Institutes for Quantum and Radiological Science and Technology, in Chiba.
"Our results should help foster international collaboration in randomized trials comparing carbon to photons/protons. The resulting data will hopefully encourage a wider expansion of carbon-ion centers around the world," he told Reuters Health by email.
Numerous studies have shown that photon radiotherapy carries a higher risk of subsequent primary cancers than surgery. Carbon-ion radiotherapy is less widely available, and the risk of subsequent primary cancers after this type of radiotherapy has remained unclear.
Dr. Makishima and colleagues examined data from 1,455 men with localized prostate cancer who received carbon-ion radiotherapy, 7,931 men treated with photon radiotherapy, and 5,948 men treated with surgery.
Second primary cancers were diagnosed within 10 years of follow-up from the date of diagnosis or treatment in 13% of patients in the carbon-ion radiotherapy group, 14% of patients in the photon radiotherapy group, and 13% of patients in the surgery group, the researchers report in The Lancet Oncology, online March 15.
After adjustment for other risk factors, the cumulative incidence of subsequent primary cancers at 9.9 years was 16.1% in the carbon-ion radiotherapy group, 24.0% in the photon-radiotherapy group and 18.7% in the surgery group.
In pairwise comparisons, the incidence of subsequent primary cancers was significantly lower in the carbon-ion radiotherapy group than in the photon-radiotherapy group, higher in the photon radiotherapy group than in the surgery group, and not significantly different between the carbon ion-radiotherapy and surgery groups.
Compared with the general population, the subsequent primary cancer risk among patients who had carbon-ion radiotherapy was not elevated significantly in any of the cancer sites, including bladder cancer, whereas the risk of bladder cancer was significantly increased among men who received photon radiotherapy.
"Interestingly, and as expected, the difference in the subsequent primary cancer risk between carbon and photon radiotherapy was limited to those cancers in the rectum and colon, which is the area that receives the high and intermediate radiation doses," Dr. Makishima said. "Also expected, smoking came out as a predictor of cancer induction in patients receiving carbon-ion radiotherapy."
"Additionally," he said, "while the initial analysis before propensity score weighting did not show any difference in subsequent primary cancer risk between surgery and carbon ion therapy, further analysis with propensity-score weighting showed a reduction in subsequent-primary-cancer risk compared to surgery, a result that is difficult to interpret."
"The results are not conclusive and require further validation through prospective data from multiple centers and nationwide cancer registries," Dr. Makishima said.
Dr. Charles N. Catton from Princess Margaret Cancer Center at the University of Toronto, Canada, who co-authored an accompanying editorial, told Reuters Health by email, "Photon radiotherapy is safe and proven treatment for prostate cancer, and the risks of a second malignancy are small. All patients should consider their options, and for those who would still prefer to avoid photon radiotherapy after an informed discussion, there are alternatives such as surgery, carbon-ion treatment, or for some, active surveillance."
"There are many factors to be weighed by patients and their physicians when deciding the best management approach for prostate cancer (that can include no immediate treatment in specific circumstances)," he said. "The risk of a second cancer from treatment is very unlikely and should not be the most important consideration, but neither should it be ignored completely."
"All patients should understand the risks of treatment and alternatives for any cancer before deciding on treatment," Dr. Catton said. "However, the risk of a second cancer following prostate photon therapy is of greater significance for those under 65 at time of treatment."
Lancet Oncol 2019.