Abstract P4-16-07: Selective use of post-mastectomy radiation therapy in the neoadjuvant setting

Abstract

Background: Neoadjuvant chemotherapy, once reserved for locally advanced breast cancer, has become more common in Stage II disease. While one of its proven benefits is an increase in the frequency of breast conserving surgery, many women will undergo mastectomy despite an excellent clinical response. Indications for post-mastectomy radiation (PMRT) following neoadjuvant therapy are not well defined. Some studies have suggested that certain subgroups of women (young age, triple negative disease) with negative nodes or 1–3 positive nodes after chemotherapy have a significant risk of local-regional failure without PMRT. We conducted a single-institution retrospective study of women undergoing neoadjuvant chemotherapy and mastectomy without PMRT to assess clinical outcomes among this cohort. Methods: 101 women with initial stage I-III disease (20% stage I, 72% stage II, 8% stage III) received neoadjuvant chemotherapy (doxorubicin-based +/− taxane) followed by mastectomy without PMRT between 2005 and 2011. Mean age was 49 years (range 22–81 years). 16% were BRCA+. 66 patients (65%) had clinically negative axillary nodes at presentation, 34% had N1 disease and 1% had N2 disease. Subtype by IHC was 61% luminal A, 11% luminal B (ER+, Her2+), 20% triple negative and 8% ER−, Her2+. At the time of surgery, 81% were node negative and 19% had 1–3 positive nodes. Pathologic complete response (pCR) (breast + axilla) occurred in 28%. Median follow-up was 34 months (range 5.5–84.5 months). Results: There were 2 (2%) local-regional failures (1 axillary recurrence at 52 months after mastectomy and 1 chest wall recurrence at 10 months). Both of these recurrences were in patients with negative nodes and luminal A tumors; patients had 2.2 and 2.5 cm of residual invasive cancer, respectively, and negative margins at mastectomy. There were no local-regional failures in women with triple negative cancers, those with 1–3 positive nodes, or patients younger than 40. Additionally, there were no failures in women with a pCR, including those with initial stage IIIA-B disease. Conclusions: Among carefully selected patients fulfilling low risk criteria for local-regional recurrence, PMRT following neoadjuvant chemotherapy may be omitted without compromising local-regional control. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P4-16-07.