Abstract P1-09-06: Save the breast after neoadjuvant therapy – identifying radiological and tumor related factors of importance for breast conserving surgery after neoadjuvant chemotherapy
Authors: Gulis Kim , Ellbrant Julia , Bendahl Pär-Ola , Svensjö Tor , Vallon-Christersson Johan , Skarping Ida Dalene , Loman Niklas , Rydén Lisa 
Published: March 2023

Background: Neoadjuvant chemotherapy (NAC) is an established treatment option in early breast cancer. NAC potentially downstages the tumor and, combined with oncoplastic techniques, may increase the eligibility for breast conserving surgery (BCS). NAC can also result in less surgical morbidity of the axilla if axillary clearance can be avoided. In addition, preoperative medical treatment allows for a thorough evaluation of treatment response and lays the foundation for adjuvant treatment decisions. The aim of the study was to prospectively estimate the proportion of BCS post NAC and the relation to well-defined factors associated with BCS post NAC.

Materials and methods: This observational prospective cohort study included 226 patients in the SCAN-B neoadjuvant cohort (Clinical trials: NCT02306096) receiving NAC between 2014 and 2019. Eligibility for BCS was based on the assessment of the surgeon at time of diagnosis and again post NAC. All the covariables were defined at time of diagnosis from mammograms and core needle biopsies, except for pathological complete response (pCR). Treatment generally consisted of 6 to 7 three-weekly treatment cycles of anthracycline- and taxane-based chemotherapy, given in sequence. In HER2-positive disease, HER2-directed antibodies were added as appropriate.The primary aim was to estimate the proportion of BCS after NAC and the secondary aim was to evaluate factors as predictors of BCS, including gene expression and surrogate molecular subtypes (St. Gallen), breast density, and other putative modifying factors.Uni- and multivariable logistic regression analysis were performed including covariates of clinical relevance and/or associated with the outcome measures (BCS versus mastectomy).

Results: The BCS rate increased during the study years, from 37% to 52%. pCR was achieved in 69 patients (30%). Predictors with a negative association to BCS were larger tumor size on mammography (T3 vs T1) (odds ratio (OR)=0.20, 95% confidence interval (CI) [0.06,0.64]), lack of visibility on ultrasound (OR=0.08, 95% CI [0.001,0.63]), lobular histological subtype vs other subtypes (OR=0,20, 95% CI [0.06,0.61)). Factors positively associated with BCS were benign axillary lymph node status (OR=2.26, 95% CI [1.26,4.06]) and surrogate molecular subtypes; patients with triple negative and HER-2 positive tumors had the highest probability of receiving BCS, 65% and 54%, respectively. Gene expression subtypes had a similar trend of being associated with BCS; patients with basal like and HER-2 enriched tumors had higher odds ratio for BCT than patients with luminal subtypes (Table 1). In the multivariable logistic regression analysis, tumor size on mammography and axillary status had the strongest association to BCS (OR=0.95, 95% CI [0.92,0.98] and OR=2.08, 95% CI [0.99,4.35], respectively).

Conclusions: Our study shows that the rate of BCS after NAC increased over the study years, but mastectomy rate in the study was still close to 50%. With increasing number of patients achieving pCR after NAC, the BCS rate should be possible to increase further. Predictors of BCS after NAC were identified, and benign axillary lymph nodes and smaller tumor size defined at time of diagnosis were the strongest predictors of BCS, supporting that initial tumor stage was important for the choice of surgery after NAC.

Table 1. Baseline characteristics and univariable logistic regression. 1. Determined by biopsy or sentinel node. 2. Only tumors visible on mammography. 3. Defined as ypT0/ypTis/ypN0.

Citation Format: Kim Gulis, Julia Ellbrant, Pär-Ola Bendahl, Tor Svensjö, Johan Vallon-Christersson, Ida Dalene Skarping, Niklas Loman, Lisa Rydén. Save the breast after neoadjuvant therapy – identifying radiological and tumor related factors of importance for breast conserving surgery after neoadjuvant chemotherapy [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-09-06.