Abstract PS2-05-30: Long-term Outcome Prediction with Residual Cancer Burden (RCB) post Neo-adjuvant Chemotherapy in Breast Cancer patients - LOPNeoRCB: An ambispective study

Abstract Aim: To study the utility of RCB in predicting outcomes of breast cancer after neoadjuvant chemotherapy. Methodology: Patients of carcinoma breast (stage 1, 2 and 3) treated in the Surgery Department after neo-adjuvant chemotherapy (NACT) from Jan 2016 to December 2023 were followed up for event free survival (EFS), distant relapse free survival (DRFS) and overall survival (OS). Demographic details, clinical course, treatment records, histopathology reports and follow-up records were collected through available digitalised hospital data, breast cancer clinic files and phone calls. Results: From January 2016 through December 2023, 654 patients were diagnosed with primary breast cancer, who received NACT upon multi-disciplinary team meeting in the Department of Surgical Disciplines of All India Institute of Medical Sciences, New Delhi, India. 124 cases were excluded. Most common molecular subtypes were HR+/Her2 Neu negative 193(36.4%) followed by Triple Negative Breast Cancer (TNBC) 156(29.4%), Triple positive breast cancer (TPBC) 91(17.2%) and HR negative/Her Positive 83(15.7%). Most of the patients had T4 disease 241(45.5%). Out of 530 patients, 335 (63.2%) had N1 disease followed by N0, N2 and N3, respectively. Most of the patients, i.e, 242 (45.6%) received anthracycline/taxane-based NACT. Following NACT, 244(46%) patients had partial response followed by complete response in 160(30%), no response in 114(21.5%) and progressive disease in 12 (2.3%) patients. 461 (87%) patients underwent mastectomy and 69(13%) underwent breast conserving surgery. In our cohort, majority of patients were negative for LVI, PNI, ENE and DCIS. Out of 323 patients with complete final histopathology with RCB, 118(36.5%) showed pCR/RCB0, RCB-2 in 99(30.6%), RCB-3 in 90(27.9%) and RCB-1 in 16(4.9%) patients. Out of 446 patients, with Miller-Payne(MP) grading, Grade5 response was seen in 143(32.1%), Grade4 in 67(15%), Grade3 in 152(34.2%), Grade2 in 63(14.2%) and Grade1 in 20(4.5%) patients. 470 (90%) patients received adjuvant radiotherapy. Hormonal therapy was received by 288(54.3%). 6-year EFS for RCB-0 was 96.6% vs RCB-3(71.1%) with HR of 9.83 (p=0.000, CI, 3.33-29.04), however there was no statistically significant difference between 0/pCR and RCB-1(p=0.07). For the MP system, prognosis of G5 was good. Lower the grade, worse the prognosis. Patients with G5 showed 95.1% 6-year’s EFS in comparison to G4-83.6%, G3- 80.3%, G2 -84.1%, G1-90% with hazards ratio (HR) of 3.11 (p=0.019, CI, 1.20-8.03), 4.16(p=0.001, CI, 1.81-9.57), 5.11 (p=0.001, CI, 1.91-13.6) and 2.05 (p=0.299, CI, 0.53-7.97), respectively. On subgroup analysis, HR-/Her2 Neu positive and TNBC were associated with worse 6- year EFS of 79.8% and 85.3%, respectively, in comparison to HR+/Her2 Neu Negative (95.1%) with increased HR, 1.91(p=0.041, CI, 1.02-3.56) and 1.34 (p=0.307, CI, 0.76-2.39) respectively. Patients with TPBC were having good EFS rate in comparison to HR+/Her2 Neu negative with HR 0.54 (p=0.213, CI, 0.20-1.42), but it wasn't statistically significant. In the whole cohort and all the molecular subtypes, the C-index was higher for RCB system in comparison to MP system except in HR-/Her2 positive in consideration of EFS and in HR+/Her 2 neu negative while considering for OS, which is suggesting that overall, the RCB was better than MP grading system in predicting long term survival outcomes in terms of EFS, DRFS and OS. RCB was better than MP in the whole cohort and HR+/Her2Neu negative while considering EFS and difference was statistically significant with p =0.04 on comparing the C- index of RCB and MP grading system with z-score test. Conclusion: The RCB score demonstrates superior prognostic accuracy over the MP grading system in predicting eEFS, DRFS and OS. Citation Format: A. P. Singh, B. K. Singh, A. Krishna , S. Mathur, V. Seenu. Long-term Outcome Prediction with Residual Cancer Burden (RCB) post Neo-adjuvant Chemotherapy in Breast Cancer patients - LOPNeoRCB: An ambispective study abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS2-05-30.