Concerns for secondary malignancy post-radiation therapy unfounded

New York-The incidence of secondary malignancies following prostate cancer therapy is similarly uncommon whether the treatment is surgery, brachytherapy, or external beam radiation therapy, report researchers from Memorial Sloan-Kettering Cancer Center, New York.

The study of 10-year-outcomes was designed to explore the validity of concerns that radiation therapy could be associated with a high incidence of secondary malignancies and that these secondary cancers carry higher mortality rates. At 10 years’ follow-up, these concerns seem to be without foundation, according to the study’s data.

“While there is a known association between radiation and the development of secondary cancers, our study indicates that the risk of these cancers following brachytherapy or external beam radiation therapy does not appear to be significantly greater than the risk associated with surgery. Some have also claimed secondary cancers in radiation-treated patients carry higher mortality rates and are uniformly lethal. We found that not to be the case. That is perhaps the more important finding,” senior author Michael J. Zelefsky, MD, chief of the brachytherapy service at Memorial Sloan-Kettering Cancer Center, told Urology Times.

“One of the implications of this study is that patients can now choose a procedure with more confidence, at least in terms of their concerns about secondary cancers,” added first author Tatiana Teslova. Teslova, a third-year medical student, presented the study at the AUA annual meeting in Atlanta, and the data were recently published in BJU International (2012; 110:1696-701).

The study looked at 10-year outcomes in 2,733 men treated with one of the three modalities between 1998 and 2001. This included 1,423 radical prostatectomy patients, 413 brachytherapy patients, and 897 external beam radiation therapy (EBRT) patients. Some 328 patients developed secondary cancers during this period.

Dr. Zelefsky said the study was unique in that the radiation was delivered with highly conformal targeting techniques that reduced exposure to surrounding normal tissues. Brachytherapy treatments consisted of permanent implantation of interstitial iodine-125 implants seeds or high-dose rate brachytherapy with iridium-192 followed at 2 months with 50 Gy fractions. EBRT consisted of intensity-modulated radiation therapy using five-field coplanar beam arrangement via 15 MV photons in daily 1.8 Gy fractions generally limited to the prostate. Patients in the study continue to be monitored closely.

Treatment type plays no significant role

The authors reported that the rates of secondary malignancies at 10 years’ post intervention were 13% for prostatectomy, 15% for brachytherapy, and 25% for EBRT. The likelihood of secondary cancers appearing within the field of treatment was 4% for prostatectomy, 2% for brachytherapy, and 4% for EBRT. The most influential variables associated with a second cancer development were older age (more prevalent in the EBRT cohort) and a smoking history. The type of treatment intervention did not play a significant role.

The 5-year secondary malignancy mortality rates were 9.6% for surgery, 7.4% for brachytherapy, and 13.1% for EBRT. Multivariate analysis comparing prostatectomy to brachytherapy and prostatectomy to EBRT found no significant differences in the ­comparisons.

Dr. Zelefsky noted that the favorable survival in this cohort of patients could be associated with diagnosing the cancers at early stages, when they were often more amenable to available therapies.

“Although the results of this study are encouraging, it remains a 10-year study as of now. Physicians and their patients need to be vigilant as to the appearance of secondary cancers whether or not they might be associated with treatment,” he added.UT