Most older women with early-stage, estrogen-positive breast cancer may benefit from receiving radiation treatment after lumpectomy, new research finds.

The study, published Monday morning in the journal Cancer, largely contradicts current breast-cancer treatment guidelines, which call for estrogen-blocker drug treatment but not radiation after breast-conserving lumpectomy surgery.

Conducted by researchers at the University of Texas MD Anderson Cancer Center, the new study set out to determine whether older women with early-stage, estrogen-positive breast cancer would have a better chance of avoiding future mastectomy if they were to receive radiation treatment after their lumpectomy.

The study explains that research published in 2004 found surgery plus six weeks of radiation provided no benefit in terms of survival or mastectomy rates over surgery followed by treatment with estrogen-blocker therapy (tamoxifen).

But, the authors point out, that study reported the findings of a clinical trial – in which participants likely complied better with their treatment regimen (i.e. taking their tamoxifen) than women typically do in the real world.

The new research looked at existing data from the National Cancer Institute’s Surveillance, Epidemiology and End Results (SEER) registry for 7,403 women ages 70 to 79 who’d had lumpectomies to treat early-stage, estrogen-positive breast cancer.

The women were diagnosed between 1992 and 2002; they were followed up through 2007. The vast majority of women – 88 percent – had received radiation treatment. Among those women, 3.2 percent had a mastectomy within 10 years of their lumpectomy. Among those who had not received radiation, 6.3 percent had a mastectomy. That represents a risk reduction of two-thirds, the study notes.

The authors observe that their analysis further found that women ages 75 to 79 whose tumors are low-grade and whose lymph nodes have been assessed for pathology are not likely to benefit from radiation and can thus likely skip that therapy.