The purpose of this work was to retrospectively evaluate survival and local control rates of triple-negative breast cancer subtypes classified as five marker negative (5NP) and core basal (CB), respectively, after breast-conserving surgery and intraoperative boost radiotherapy with electrons (IOERT) followed by whole breast irradiation.
A total of 71 patients with triple-negative breast cancer were enrolled, who were treated with lumpectomy, axillary lymph node dissection, and IOERT with 9.6 Gy (median Dmax) followed by normofractionated whole breast irradiation to median total doses of 54 Gy. Chemotherapy was applied in a neoadjuvant (12 %), adjuvant (75 %), or combinational setting (7 %).
After a median follow-up of 97 months (range 4-170 months), 5 in-breast recurrences were detected (7.0 %). For all patients, 8-year actuarial rates for local control, metastases-free survival, disease-specific survival, and overall survival amounted to 89, 75, 80, and 69 %, respectively. All local recurrences occurred in grade 3 (G3) tumors irrespective of their specific immunohistochemical phenotype; thus, the local control rate for grades 1/2 (G1/2) was 100 % for both 5NP and CB, while for G3 it was 88 % for 5NP and 90 % for CB (p = 0.65 and 0.82, respectively, n.s.). For disease-specific survival, only the difference of the best-prognosis group 5-NP/G3 vs. the worst-prognosis cohort CB/G1/2 was statistically significant: 90 % vs. 54 % (p = 0.03).
Boost-IOERT provides acceptable long-term in-breast control in triple negative breast cancer. The best subgroup in terms of disease-specific survival was represented by 5NP in combination with tumor grading G3.