Most older women with early breast cancer are more likely to avoid eventual mastectomy if they undergo radiation therapy after lumpectomy, according to a recent evaluation of 10-year outcomes that contradicts clinical recommendations.

Previous research has indicated that radiation therapy does not lower the risk of mastectomy and could therefore be omitted in older women with stage I, estrogen receptor (ER)-positive breast cancer who undergo conservative surgery (lumpectomy), recounted investigators Benjamin D. Smith, MD, and colleagues in the current report, published by the journal Cancer. National treatment guidelines advise that older women with early-stage, ER-positive disease undergo lumpectomy followed by estrogen-blocking therapy alone, and not radiation therapy.

To explore whether the earlier findings applied to women outside of clinical trials, Smith, of The University of Texas MD Anderson Cancer Center in Houston, and his fellow researchers used the Surveillance, Epidemiology, and End Results–Medicare observational cohort to determine the effect of radiation therapy on the risk of mastectomy among older women with stage I, ER-positive breast cancer. They identified 7,403 such patients, aged 70 to 79 years, who underwent lumpectomy between 1992 and 2002. Approximately 88% of those women received radiation therapy after their surgery.

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At a median follow-up of 7.3 years, the risk of subsequent mastectomy within 10 years of diagnosis was 3.2% for women who received radiation therapy and 6.3% for those who did not. In adjusted analyses, radiation therapy was associated with a lower risk of mastectomy (hazard ratio 0.33).

Radiation therapy was associated with an absolute reduction in risk of mastectomy that ranged from 4.3% to 9.8% at 10 years for all subgroups except that of patients aged 75 to 79 years without high-grade tumors and with a pathologic lymph node assessment.