Radiotherapy for prostate cancer (PCa) is no more likely than radical prostatectomy (RP) to result in secondary cancers, a new study suggests.

In addition, the secondary cancers that develop after radiotherapy are not more lethal than those that develop after RP, according to an online report in BJU International.

The findings dispel a number of misconceptions regarding the frequency and presumed behavior of secondary malignancies (SMs) in patients treated with radiotherapy, Michael J. Zelefsky, MD, and colleagues at Memorial Sloan-Kettering Cancer Center in New York stated.

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In a retrospective study of 2,658 patients with localized PCa treated at their center—including 897 treated with external beam radiotherapy (EBRT), 413 treated with brachytherapy (BT), and 1,348 treated with RP—the researchers found that the 10-year likelihoods for secondary bladder or colorectal cancer development in the EBRT, BT, and RP groups were 4%, 2%, and 3%, respectively, a non-significant difference between groups.

Among 243 patients who developed an SM, the five-year likelihood of SM-related mortality in the EBRT and BT groups was 43.7% and 15.6%, respectively, compared with 26.3% in the RP cohort. The differences among the groups were not significant.

The 10-year secondary malignancy (SM)-free survival for the EBRT, BT, and RP cohorts were 83%, 89%, and 87%, respectively. Compared with RP, EBRT was associated with significantly worse SM-free survival and BT was not.

Older age and a history of smoking were significant predictors for SM development.

The researchers observed that the lower incidence of secondary bladder and colorectal cancers found in their study could possibly be related to the highly targeted nature of the radiotherapy delivery (e.g., intensity-modulated radiotherapy) used at their institution.

Dr. Zelefsky’s group stated that the limitations of their study include its retrospective design and the relatively small number of patients. They noted that SM is a relatively rare event. The authors acknowledged that longer follow-up observations will be necessary to corroborate their findings.