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Less Is More: Postoperative Radiation May Be Avoided in Older Women With Estrogen Receptor–Rich Tumors

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Key Points

  • Postoperative radiation is the standard of care for all patients who undergo breast-conserving surgery and endocrine therapy.
  • The PRIME II study has found that whole-breast radiation therapy may be avoided in some older women with hormone receptor-positive tumors following surgery and neoadjuvant hormone therapy.
  • For patients with low levels of estrogen receptor expression, radiation should remain standard of care.

Among older women with hormone receptor–positive breast cancer, it is reasonable to omit whole-breast radiation therapy after breast-conserving surgery and neoadjuvant hormone therapy if the patient’s tumors have high levels of estrogen receptor expression, but radiation should remain standard of care for those with low levels of estrogen receptor expression. These findings of the PRIME II study were reported at the 2013 San Antonio Breast Cancer Symposium (Abstract S2-01).

“Postoperative radiation is the standard of care for all patients who undergo breast-conserving surgery and endocrine therapy, irrespective of risk factors and age. This study is very likely to change practice in the United Kingdom. Older patients find radiation therapy burdensome, and some may have to travel long distances to get it,” said Ian Kunkler, MD, Edinburgh Cancer Research Center, University of Edinburgh, Scotland.

“The study is also likely to change practice in the United States,” agreed press conference moderator Kent Osborne, MD, Director of the Dan L. Duncan Cancer Center and the Lester and Sue Smith Breast Center at Baylor College of Medicine, Houston.

PRIME II Trial

The multicenter study was conducted at 98 sites across six countries and had a median follow-up of 5 years. The trial included 1,356 patients aged 65 and older with histologically confirmed grade 1 and 2 cancer (tumor size up to 3 cm) who were randomly assigned to whole-breast radiation therapy or no whole-breast radiation therapy following breast-conserving surgery and neoadjuvant endocrine therapy.

The 5-year actuarial local recurrence rate was 4.1% in those who did not receive whole-breast radiation therapy vs 1.3% in those who did. An unplanned analysis of estrogen receptor status revealed that whole-breast radiation therapy was most effective in women with tumors that had low levels of estrogen receptor expression. Among those with high levels of estrogen receptor expression, local recurrence rate was 3.2% in the no whole-breast radiation therapy group vs 0.8% in those who received whole-breast radiation therapy (P = .0003), whereas in the low estrogen receptor group, local recurrence rates were 11.1% vs 0%, respectively (P = .015).

A multivariate analysis showed that not receiving radiotherapy and low estrogen receptor expression were significant predictors of recurrence (P = .001, and P = .02, respectively).

Overall survival was not significantly different between those who did not receive whole-breast radiation therapy (93.8%) and those who did (94.2%). Dr. Kunkel said that 73% of the deaths that occurred were not related to breast cancer.

Compliance Issues to Be Addressed

During the question-and-answer session after the presentation, Steven Vogl, MD, a medical oncologist in the Bronx, New York, said that compliance with hormone therapy is important, and there was no way to know whether patients were actually taking their hormone therapy from the data presented. Dr. Kunkler said those data were not yet analyzed but would be included in the journal publication of the study.

This study was funded by the Chief Scientist’s Office for Scotland. Dr. Kunkler declared no potential conflicts of interest.

 

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.


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