Brachytherapy has mixed results as breast cancer treatment

Brachytherapy has mixed results as breast cancer treatment

5/2/2014

Research after lumpectomy showed that older breast cancer patients were more likely to undergo mastectomy after brachytherapy, compared to external-beam radiation therapy (EBRT). However, they fared better than those who did not receive any radiation.

Five years after initial treatment for early breast cancer, 2.8% of patients treated with brachytherapy had undergone mastectomy compared with 1.3% of patients who had EBRT. Both rates were lower than the mastectomy rate among women who had lumpectomy without adjuvant radiation therapy (4.7%).

Patients who met American Society of Radiation Oncology (ASTRO) suitability criteria for brachytherapy had mastectomy rates similar to those of patients who had EBRT, as reported online in the International Journal of Radiation Oncology Biology*Physics.

"The takeaway message to both physicians and older breast cancer patients is that, in general, all of these patients did well with very high likelihood of breast preservation," Benjamin Smith, MD, of the University of Texas MD Anderson Cancer Center in Houston, said in a statement.

"However, the likelihood of breast preservation was best with external-beam radiation, worst with no radiation, and in between with brachytherapy."

The results are consistent with those that Smith and colleagues have previously reported.

Brachytherapy to the lumpectomy cavity offers certain advantages over EBRT, including convenience and reduced exposure to radiation. Those advantages have fueled rapid growth in use of the treatment in recent years.

But some breast cancer specialists have remained unconvinced that breast brachytherapy leads to outcomes comparable to those of EBRT, particularly given the lack of patient-specific evidence to identify the most appropriate candidates.

To guide use of brachytherapy in clinical practice, ASTRO proposed suitability criteria. "Suitable" patients have low-risk characteristics and favorable local disease control. Patients who fall into the categories of "cautionary" have some high-risk characteristics associated with a reduced likelihood of favorable outcomes, and "unsuitable" patients do not meet criteria for breast brachytherapy.

However, the ASTRO criteria have not been empirically validated for ability to stratify patients into risk categories, Smith and co-authors noted. Moreover, some authorities have suggested that some low-risk patients might avoid radiation therapy altogether.

Smith and colleagues have performed several retrospective cohort studies to evaluate outcomes with breast brachytherapy and to compare the modality to whole-breast EBRT. The most recent study included 36,000 women identified through the Surveillance, Epidemiology, and End Results-Medicare linked database.

The women had new breast cancer diagnoses during the years 2002 to 2007 and all of them were older than 65. The study population consisted of 28,718 patients with invasive breast cancer and 7,229 with ductal carcinoma in situ. Overall, 1,310 patients had brachytherapy, 8,254 had lumpectomy alone, and about 26,383 opted for EBRT.

The cohort had a median follow-up duration of 3.5 years. As compared with patients who had no radiation therapy, the brachytherapy group had a 39% reduction in the hazard for mastectomy and EBRT had a 78% reduction in hazard.

Brachytherapy was associated with higher rates of treatment-related adverse events compared with EBRT, including postoperative infection (16.5% versus 11.4%), breast pain (22.9% versus 16.7%), and fat necrosis (15.3% versus 7.7%). Patients who had lumpectomy alone had the lowest complication rates.

In the subgroup of patients with invasive breast cancer, 34.7% met ASTRO criteria for brachytherapy suitability, 17.6% were in the cautionary category, and 35.2% were unsuitable. The remaining 12.5% were unclassified. The authors found that 55% of patients treated with brachytherapy were suitable by the ASTRO criteria.

Analysis of mastectomy risk by ASTRO category, irrespective of treatment, showed that patients in the cautionary and unsuitable categories had a significantly increased risk of mastectomy compared with suitable patients (HR 1.61, P<0.001 for cautionary; HR 1.34, P=0.03 for unsuitable).

In the suitable subset of patients, brachytherapy compared favorably with EBRT, as 5-year mastectomy rates were 1% and 0.8% respectively.

"Within each ASTRO group, EBRT consistently showed the lowest subsequent mastectomy risks versus lumpectomy alone, whereas brachytherapy consistently showed intermediate subsequent mastectomy risks versus lumpectomy alone," the authors said of their findings.

The authors of an accompanying editorial cited several limitations of the study, including the fact that the time period (2002 to 2007) represents an early period of brachytherapy adoption. Technology and dosimetry limits have improved substantially since then, said Robert Kuske, MD, of Arizona Breast Cancer Specialists in Scottsdale, and S. Stanley Young, PhD, of the National Institute of Statistical Sciences in Research Triangle Park, N.C.

Limiting the analysis to older patients also limits the applicability of the results, particularly attempts to evaluate outcomes by ASTRO suitability criteria.

"The larger scientific body of literature supports the continued use and study of brachytherapy accelerated partial breast irradiation (APBI), and this study should not slow down its momentum," said Kuske and Young. "Multiple randomized, prospective clinical trials have been completed, with maturing data, so ultimately we will have a scientifically valid head-t0-head comparison of APBI versus whole-breast irradiation."

 

Source: MedPage Today: http://www.medpagetoday.com/HematologyOncology/BreastCancer/44164