Accelerated Partial-Breast Irradiation Effective in Subtypes

September 16, 2011 — Five-year outcomes after accelerated partial-breast irradiation (APBI) were "excellent" in a number of breast cancer subtypes that tend to have poorer prognoses, according to presenters at the 2011 Breast Cancer Symposium (BCS) in San Francisco, California.

J. Ben Wilkinson, MD, and colleagues from the Beaumont Cancer Institute in Royal Oak, Michigan, evaluated 516 consecutive patients with early breast cancer who received APBI. The mean age of the participants was 66 years and median follow-up was 4.9 years.

The patients received APBI via interstitial brachytherapy (n = 221), balloon-based brachytherapy (n = 201), or 3-dimensional conformal radiation therapy (n = 106).

Tumors were classified according to estrogen-receptor (ER) status, progesterone-receptor (PR) status, and human epidermal growth-factor (HER-2/neu)-receptor status. Patients lacking test results for all 3 receptors were excluded.

Of the 278 eligible patients, 164 had the luminal A subtype (ER positive, PR positive/negative, and HER-2 negative; 81 had the luminal B subtype (ER positive, PR positive/negative, and HER-2 positive); 5 had the HER-2 subtype; and 28 had the basal subtype (ER negative, PR negative, and HER-2 negative). The researchers estimated ipsilateral breast tumor recurrence, regional node failure, distant metastasis, disease-free survival, cause-specific survival, and overall survival. All of the subgroups had similar margin and nodal status.

The basal and HER-2 subtype patients had higher histologic grades, larger tumors, and were more likely to have received chemotherapy. Basal subtype patients were more likely to have been African American (18% vs 4% luminal A/luminal B; P = .002).

At 5 years, ipsilateral breast tumor recurrence rates ranged from 0.0% to 4.8%, but were not significantly different among the subtypes. Distant metastasis was seen only in the luminal A (2.5%) and luminal B (1.4%) subtypes (P = .87).

Disease-free survival (95% to 100%), cause-specific survival (97% to 100%), and overall survival (80% to 100%) were not statistically different among the breast cancer subtypes.

The researchers concluded that "5-year local control rates after treatment with APBI are excellent for luminal, HER2, and triple-negative phenotypes of early-stage breast cancer. Further study of breast cancer subtypes is important and may be useful when counseling patients on adjuvant treatment options following breast-conserving surgery."

H. Joseph Barthold, MD, from Commonwealth Hematology Oncology in Boston, Massachusetts, and who is a member of the BCS news planning team, noted that "while awaiting the completion and publication of the randomized trial, the group at Beaumont — who have long been leaders in this field — have shown that this approach is equally appropriate in various subsets of breast cancer patients.... Partial-breast radiation will continue to be offered as an alternative therapy/option approach to selected low-risk groups. Published data now show it to be equivalent to more protracted radiation schedules."

Dr. Wilkinson and Dr. Barthold have disclosed no relevant financial relationships.

2011 Breast Cancer Symposium (BCS): Abstract 83. Presented September 8, 2011.

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