Luminal A breast cancer may not need radiation

By Fran Lowry

NEW YORK (Reuters Health) – Older women, particularly those over the age of 60, may not need local breast radiation if they have the luminal A subtype of breast cancer, according to new research presented Sunday in Chicago at the annual meeting of the American Association for Cancer Research.

“This is an observational study and we have to be 200% sure before we can recommend that women with this breast cancer subtype can safely go without radiation but our current observations do suggest that luminal A breast cancer in older women may not require radiation,” lead author Dr. Fei-Fei Liu, from Princess Margaret Hospital and the University of Toronto, Toronto, Canada, told Reuters Health.

Dr. Liu and her colleagues performed molecular subtyping for estrogen receptor (ER), progesterone receptor (PR), HER2, Ki-67, epidermal growth factor receptor and cytokeratin 5/6 on 304 tumor blocks that were taken from 769 postmenopausal women with T1 and T2 node negative breast cancer.

Based on the immunohistochemistry results, the patients were classified into six categories: luminal A, luminal B, luminal-HER2, HER2-enriched, basal-like or triple-negative phenotype-nonbasal.

The women had all been participants in a randomized trial that was conducted from December 1992 to June 2000, where they were assigned to tamoxifen and whole-breast radiation therapy, or to tamoxifen alone.

The median follow-up was 10 years. In the group as a whole, the ipsilateral breast tumor recurrence rate at 10 years was 13.8% with tamoxifen alone, compared with 5.0% with tamoxifen plus radiation.

When stratified by molecular subtype, women in the luminal A subgroup (defined as ER-positive, PR-positive, HER2-negative and low Ki-67 score) had the best outcome, with a 10-year risk for local relapse of 8% with tamoxifen alone vs. 4.6% with tamoxifen and breast radiation therapy.

For luminal A patients older than 60 (n=103) the local breast relapse rate was 4.3% for tamoxifen alone vs 6% for tamoxifen plus breast radiation therapy.

“When you add the radiation to this group there is absolutely no advantage,” Dr. Liu said.

She added that about 25% of newly diagnosed breast cancer patients might fall into the luminal A category, and that her findings have the potential to be practice changing and also to save the health care system a lot of money.

“We’ve done some back of the envelope calculations about the potential saving in health care dollars. In Ontario where there are 9,000 new breast cancer patients diagnosed each year, and each course of radiotherapy costs about eight thousand dollars, we estimate that forgoing the radiation would save about 20 million dollars. In the US, it would be about 400 million per year,” Dr. Liu said.

Dr. William Wong, from the Mayo Clinic, Scottsdale, Arizona, told Reuters Health that the observation is “very interesting and important” but the results are not yet conclusive.

“Only 304 of the tissue blocks from the original cohort were available, and the numbers get smaller and smaller, and so by the time they looked at the luminal A in women older than 60, they were down to 103 patients. That is too small a number to make any definite conclusions,” Dr. Wong said.

“In order to be the new standard of care the observation needs to be validated in a large trial that looks specifically at this subtype,” he said.