SAN FRANCISCO – Ten years of follow-up showed no significant difference in breast cancer locoregional recurrence, distant metastasis, or survival rates in 274 patients treated with accelerated partial breast irradiation compared with 274 matched patients treated with whole breast irradiation.
The data came from records on 3,009 patients with early-stage breast cancer who were treated with breast-conserving therapy at one institution between 1980 and 2012.
Four percent in each group developed local recurrence, 1% in each group had a regional recurrence, and 6% had distant metastases after partial breast irradiation and 3%, after whole breast irradiation. There was a nonsignificant statistical trend toward a higher rate of contralateral breast failure in the whole breast irradiation group (9%) compared with the partial breast irradiation group (3%, P = .06), Dr. Jessica Wobb reported in a poster presentation at a breast cancer symposium sponsored by the American Society of Clinical Oncology.
Rates of disease-free survival were 91% in the partial breast irradiation group and 93% in the whole breast irradiation group. Cause-specific survival rates were 93% and 94%, respectively, and overall survival rates were 75% and 82%, reported Dr. Wobb of the Beaumont Cancer Institute, Royal Oak, Mich. None of these differences reached statistical significance.
This is one of the first reports on prolonged follow-up after accelerated partial breast irradiation, she noted. Mean follow-up was 7.8 years after partial breast irradiation and 8.1 years after whole breast irradiation, a difference that was statistically significant, but amounted to less than 4 months. All patients were followed for at least 1 year.
Patients in the cohorts were matched by age (within 3 years); T stage (Tis, T1, or T2); and estrogen receptor (ER) status. The mean age was 63 years of age in both groups. Eighty-eight percent in both groups had ER-positive tumors. The stage distribution in both groups consisted of 18% with stage Tis tumors, 71% with T1 tumors, and 11% with T2 tumors.
Significantly fewer patients in the partial breast irradiation group received adjuvant hormonal therapy (54%) compared with those in the whole breast irradiation group (68%). There was a trend toward smaller tumors in patients undergoing partial breast irradiation than in those receiving whole breast irradiation, with mean tumor sizes of 11.4 mm and 13 mm (P = .06).
Other characteristics were similar between the groups, including the proportion with negative lymph nodes (91% of patients undergoing partial breast irradiation and 86% of those who got whole breast irradiation), the proportion with negative final margins (94% and 95%, respectively), and the proportion who received adjuvant chemotherapy (15% and 18%).
Close tumor margins increased the risk for ipsilateral breast tumor recurrence in both groups, and positive margins increased the recurrence risk in the whole breast irradiation group, a univariate analysis found.
Dr. Wobb reported having no relevant financial disclosures.
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