Long-Term Outcome of Novel Intraoperatively-Placed Brachytherapy for Rapid Completion of Breast Conserving Therapy

Abstract

<h3>Purpose/Objective(s)</h3> To evaluate the long-term outcome of accelerated partial breast irradiation utilizing an intraoperatively-placed applicator-based brachytherapy (ABB) in early-stage breast cancer. <h3>Materials/Methods</h3> We identified 226 patients with pTis-T2, pN0/pN1mic breast cancer treated with ABB at our institution 10/2012-9/2019 from our prospective registry, of whom 223 had follow-ups (FU) at our institution and form the basis of this analysis. ABB initiated at a median of two days following operation. The median treatment duration including surgery and ABB completion was 7 days. The prescribed dose regimens were as follows: 32 Gy in 8 twice-daily fractions (n=25), 34 Gy in 10 twice-daily fractions (n=99), and 21 Gy in 3 once-daily fractions (n=99). After completion of ABB, adjuvant endocrine treatment (ET) was prescribed for patients with hormone receptor-positive (HR+) tumors. ET adherence was defined completion of planned ET course or ≥ 80% of FU period. Cumulative incidence of ipsilateral breast tumor recurrence (IBTR) and disease-free survival (DFS) were estimated using Gray's test, with death as a competing risk. Variables influencing for IBTR-free survival rate (IBTRFS) were analyzed by Fine-Gray model. <h3>Results</h3> 221/226 patients had HR+ tumors, including 38 (17.0%) with Tis and 185 (83.0%) with invasive cancers. After a median follow-up of 63 months (interquartile range, 42 – 81), 20 (9.0%) patients recurred, including 18 (8.1%) with an IBTR. The site of recurrence was IBTR alone in 16 patients, simultaneous IBTR/regional/distant metastasis (DM) in 2, regional recurrence in 1, and DM in 1 patient. 5-year IBTRFS and DFS were 91.6% and 91.1%, respectively. IBTR was significantly lower for post-menopausal women and those adherents to prescribed ET: menopause (HR 0.26, 95% CI 0.09 – 0.76, p < 0.01) and ET adherence (HR 0.19, 95% CI 0.04 – 0.80, p = 0.01). The 5-year IBTRFS for post-menopausal patients (n=204) was significantly higher than for non-menopausal women (n=19) (93.5% vs. 65.3%, p < 0.01). The 5-year IBTRFS in ET-adherent patients (n=96) was significantly better than for ET-non-adherent patients (n=127) (97.5% vs. 87.7%, p = 0.01). IBTRFS was not different by ABB regimens (HR 0.61, 95% CI 0.28 – 1.33, p = 0.21). <h3>Conclusion</h3> ABB is an attractive option for patients with favorable early-stage breast cancer. Post-menopausal status and adherence to prescribed ET predicted favorable outcomes in terms of IBTRFS after ABB. Our results highlight the importance of multidisciplinary counseling with careful patient selection for ABB and encouragement of ET compliance.