Radiation therapy therapy (RT) reduced the risk of subsequent mastectomy for women ages 70 to 79 with Stage 1, estrogen receptor-positive breast cancer who underwent conservative surgery, according to a study published Aug. 13 in Cancer. The findings contradict a previous clinical trial, which suggested that RT did not lower the risk of subsequent mastectomy or death from breast cancer.

“For older patients in particular, the benefits of adjuvant therapies intended to prevent a future recurrence must be weighed against the competing risk of noncancer death before recurrence,” wrote Jeffrey M. Albert, MD, from the department of radiation oncology at MD Anderson Cancer Center in Houston, and colleagues.

CALGB 9343, a clinical trial of women 70 years of age and older with Stage 1, estrogen receptor-positive breast cancer who underwent conservative therapy and received tamoxifen, randomized patients into an RT and a no RT cohort. At 10 years of follow-up, the researchers observed RT had lowered the risk of local recurrence, but it did not significantly lower the risk of subsequent mastectomy or death from breast cancer. Thus, the researchers concluded RT could be omitted for these patients.

However, Albert and colleagues noted the existence of important differences between women in clinical trials and those in routine practice. A clinical trial population may be more likely to adhere to endocrine therapy, and there are differences in imaging standards, surgical specimen labeling and pathologic assessment details in the clinical practice and community settings. Thus, they hypothesized that the risk of subsequent mastectomy and reduction in risk after RT are greater in routine practice than in the clinical trial setting.

In the current study, the researchers used the Surveillance, Epidemiology and End Results (SEER)-Medicare observational cohort as their data source and analyzed outcomes for 7,403 women ages 70 to 79 who underwent conservative surgery between 1992 and 2002. A total of 6,484 women received RT. Median follow-up was 7.3 years.

The 10-year risk of mastectomy was 3.2 percent in patients who received RT and 6.3 percent in women who did not, which is a statistically significant relative reduction. The reduced risk was consistent across most variables.

“Our findings further suggest that baseline clinical-pathologic features may help to identify patients who are most and least likely to benefit from RT,” wrote Albert et al.

Women with high-grade breast cancer derived a 6.7 percent absolute reduction in the 10-year risk of mastectomy; patients who underwent clinical lymph node assessment derived a 4.9 percent absolute reduction and those ages 70 to 74 years old derived a 3.8 percent absolute reduction.

On the other hand, women ages 75 to 79 who did not have tumors with high-grade histology and who underwent pathologic lymph node assessment did not benefit from RT. This finding, coupled with previous clinical trial data, could allow patients in this category to choose conservative surgery without RT rather than mastectomy.

The researchers examined the implications in light of demographic trends, particularly the expected 57 percent increase in the number of breast cancers expected to be diagnosed in older women in the next 20 years. Although older patients need to balance the benefits of a future recurrence with the risk of noncancer death, Albert and colleagues reported 61 percent of patients in this cohort had no comorbid illness, and 66 percent of these patients survived at least 10 years after diagnosis. “The life expectancy of such patients, thus, is sufficiently long to justify consideration of RT.”