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ESTRO 38: Long-Term Results of Adjuvant Radiotherapy Plus Antihormonal Treatment in Hormone Receptor–Positive Breast Cancer

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Key Points

  • Cancer did not recur in the same breast in 97.5% of women who had whole-breast irradiation (WBI) and in 92.4%  of women who did not have WBI (P < .01).
  • After an average median follow-up of nearly 10 years, there were 10 in-breast recurrences among the 439 women who had WBI and 31 among the 430 women who only had antihormonal treatment.
  • There was a significantly higher disease-free survival rate of 94.5% among those who had WBI, compared to 88.4% among those who did not.

Women with early-stage, low-risk, hormone receptor–positive breast cancer may be less likely to experience disease recurrence if they have radiotherapy after surgery as well as antihormonal treatment, according to results from a trial that has followed 869 women for 10 years. These findings were presented by Fastner et al at ESTRO 38, the annual congress of the European Society for Radiotherapy & Oncology (ESTRO) (Abstract OC-0270).

ABCSG 8A Trial

The Austrian Breast and Colorectal Cancer Study Group (ABCSG) 8A trial recruited 869 postmenopausal women between 1996 and 2004. Patients were randomly assigned to receive either whole-breast irradiation (WBI) or antihormonal treatment alone after breast-conserving surgery. The patients had early, low-risk tumors that were either grade 1 or 2, less than 3 cm in diameter, and without any cancer cells identified in the lymph nodes. The tumors were driven by hormones such as estrogen or progesterone and so would respond to antihormonal therapies such as tamoxifen or anastrozole. The patients had received no previous chemotherapy, radiotherapy, or hormone therapy.

WBI was given up to a total average dose of 50 Gy over a period of 39 days and within 6 weeks of surgery; 71% of patients also received an additional boost of an average of 10 Gy to the tumor bed.

If cancer had spread the sentinel lymph node under the arm, then the sentinel node would also be removed during surgery, together with axillary lymph nodes. In cases where no tumor cells were found in the sentinel lymph node, removal of additional axillary nodes was omitted.

Results

New findings from the 8A trial showed that cancer did not return in the same breast in 97.5% of women who had WBI and in 92.4% of women who did not have WBI (P < .01). After an average median follow-up of nearly 10 years, there were 10 in-breast recurrences among the 439 women who had WBI and 31 among the 430 women who only had antihormonal treatment. There was a significantly higher disease-free survival rate of 94.5% among those who had WBI, compared to 88.4% among those who did not. Advantage in DFS after WBI was also observed after sentinel node extirpation only (hazard ratio [HR] = 0.25, P = .007) but not after axillary dissection (HR = 0.7, P = .2).

The cost, logistics, and possible adverse side effects associated with WBI have led researchers to try to identify a subgroup of patients with breast cancer who might not need radiotherapy. However, these latest results suggest this might not be possible.

First study author Gerd Fastner, MD, Associate Professor at the University Clinic of Radiotherapy and Radio-Oncology, University Hospital, Paracelsus Medical University in Salzburg, Austria, told the conference, “Our findings show that radiotherapy is still highly effective in significantly improving local control and disease-free survival in combination with [antihormonal therapy] compared to [antihormonal therapy] alone. This remains true after long-term follow-up of patients with breast cancer with a good prognosis. In our analysis, the omission of WBI turned out to be the main predictor for in-breast recurrences.”

“In addition, tumors that could not have their grade classified had a nearly four-fold risk of recurring, which might be due to some of the tumors being more aggressive.”

Overall survival and metastasis-free survival were similar between women who did or did not have WBI. “Improving control of the tumor at the primary site may translate into better survival in future years,” said Dr. Fastner.

A later analysis of tissue from 519 of the patients, which looked at levels of Ki-67 and HER2 found that patients who had high levels of Ki-67 (above 20%), or who were HER2-positive, or both, did not have a higher risk of the cancer returning to the same breast, although there was a clear trend towards it.

“This finding requires further research in larger groups of women with longer follow-up, as this could be a chance finding because of the small numbers of women for whom we had this information,” said Dr. Fastner.

He concluded, “We believe that the additional benefits of postoperative radiotherapy have been confirmed in hormone receptor–positive patients, regardless of whether or not they are at high risk of breast cancer recurrence. In the light of current knowledge, this does not necessarily mean that they have to have whole breast irradiation nowadays, since partial breast irradiation has proved to be competitive. Partial breast irradiation can be carried out with postoperative hypofractionated external beam radiotherapy, intraoperative techniques, or perioperative brachytherapy. The total omission of radiotherapy should only be considered in frail, elderly patients who would not be able to tolerate such treatment.”

Disclosure: For full disclosures of the study authors, visit estro.org.

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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