Abstract PD16-03: Use of post-neoadjuvant chemotherapy image-guided breast vacuum assisted biopsy to predict residual cancer in exceptional responders: A prospective cohort study

Abstract Background: Post-neoadjuvant chemotherapy (NAC) image-guided biopsy of the residual imaging abnormality/tumor bed is increasingly used to assess residual disease in the breast and potentially identify exceptional responders who may not require surgical intervention. Previous studies have shown variable results on the diagnostic performance of this technique. The aim of this analysis was to assess the accuracy of post-NAC, image-guided vacuum assisted biopsy (VAB) to predict residual disease in the breast using a standardized assessment protocol. The findings could help further support the optimal design of trials omitting surgery in selected patients. Methods: Prospective cohort study (BR154b) of consecutive patients with HER2 positive and triple negative (TN) invasive ductal carcinoma (IDC), treated with NAC, who underwent post-NAC VAB to aid surgical planning between 02/2018 and 06/2022 at one institution. Patients with complete/near complete imaging response (residual imaging abnormality ≤ 2cm) had a VAB to sample ≥ 90% of the breast residuum/tumor bed previously marked by clip insertion. Biopsy samples were defined as representative if pathology features suggestive of tumor bed or residual cancer were identified. Pathologic complete response (pCR) was defined as no residual invasive or in situ disease in the breast (ypT0). Diagnostic accuracy of VAB was calculated using final surgical pathology as the reference standard. Simple descriptive statistics were used. Results: A total of 54 women met the eligibility criteria and underwent post-NAC VAB. This was not representative in 3 cases and therefore 51 women were included in the analysis. Median age was 49 years [interquartile range (IQR): 43 – 61]. The majority of cancers were grade 3 (n=31) or grade 2 (n=19). Subtype distribution was 21 (41.2%) for hormone receptor (HR) positive/HER2 positive, 13 (25.5%) for HR negative/HER2 positive and 17 (33.3%) for TN IDC. There was associated DCIS at diagnosis in 37.3% of cases. The majority of the cancers at presentation were T2 (n=35, 68.6%) with a median tumor size on imaging of 28 mm (IQR: 28 – 43). There were associated microcalcifications in 29 cases (n=11 extending beyond the main tumor). Sixteen women presented with cN+ disease. On completion of NAC, 19 women had complete imaging response, while in the remaining the median size of the residual imaging abnormality was 12 mm (IQR: 9 – 16). A post-NAC VAB was performed with ultrasound or stereo-guidance in 48 and 3 cases respectively. The median size (gauze) of needle used was 10 (IQR: 10) and the median number of cores obtained was 8 (IQR: 6-8). In the surgical specimen, the overall breast pCR rate was 58.8% (52.4% for HR positive/HER2 positive, 76.9% for HR negative/HER2 positive and 52.9% for TN). The axillary pCR rate was 81.25%. The false negative rate (FNR) of post-NAC VAB was 4.76% (1/51, 95% CI: 0.12 – 23.82%). The sensitivity and specificity for residual disease were 95.24% (95% CI: 76.18 – 99.88) and 93.33% (95% CI: 77.93 – 99.18) respectively. The negative predictive value was 96.55% (95% CI 80.49 – 99.48) and the overall accuracy 94.12% (95% CI: 83.76 – 98.77). Conclusions: This analysis suggests that a standardized assessment protocol using image-guided VAB in patients with HER2 positive or TN IDC and exceptional response to NAC (residual imaging abnormality/tumor bed measuring ≤ 2 cm) aiming to sample ≥ 90% of the breast residuum allows reliable prediction of residual disease and breast pCR with a FNR < 5%. These results further support the optimal design of de-escalation trials in NAC exceptional responders testing the safety of omitting surgery. Citation Format: Marios Konstantinos Tasoulis, Romney Pope, Tanja Gagliardi, Ashutosh Nerurkar, Alicia F. Okines, Nicholas Turner, Fiona MacNeill. Use of post-neoadjuvant chemotherapy image-guided breast vacuum assisted biopsy to predict residual cancer in exceptional responders: A prospective cohort study [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 PD16-03.