Abstract P2-16-25: Young age breast cancer who achieve pathologic complete response after neoadjuvant chemotherapy display excellent outcome than older age breast cancers

Introduction: Patients with pathologic complete response (pCR) after neoadjuvant chemotherapy (NCT) is known to have a good prognosis compared with patients with no residual disease necessitating additional adjuvant systemic therapy for some population. Also there are cases of recurrence and/or death among patients with pCR. We aimed to 1)analyze whether prognostic impact of pCR differ across subtypes and age groups and 2)investigate factors associated with outcome after achieving pCR. Methods: Among 1930 patients who underwent NCT at Asan Medical Center between 1890 to 2018, 1688 patients with clinico-pathological, follow-up data available were analyzed. 339 (20.1%) patients had pCR defined as ypT0/Tis with no residual nodes(N0) after NCT. Pathologic CR rate were 10.2% (102/1003), 40.0% (100/250) and 31.6% (137/434) in each HR positive, HRneg/HER2pos and triple negative tumors. Pathologic CR rate were 19.7% (232/1175) and 20.9% (107/513) in young age and old age group respectively. Results: Median follow up period was 62 months (6-129 months). Five-year disease free survival (5yr-DFS) of ‘total’ patients and patients with ‘no-pCR’ and ‘pCR’ were 81.7%, 79.1% and 92.4% respectively (p= Among patients with pCR, residual in-situ disease (p= 5cm (p=0.006, HR=1.45), and negative hormone receptor (p Intriguingly, magnitude of impact affecting prognosis differed by age groups that younger patients (≤50) who achieved pCR displayed excellent outcome similar to older age group (HR=1.33, CI 0.57-3.12, p=0.51). On the other hand, young age patients who did not achieve pCR had the worst outcome with 5yr-DFS 77.3% indicating the necessity of additional systemic therapy. Also, while HR negative tumors are known to have worse outcome, HRneg/pCR group had longer 5yr-DFS than HRpos/no-pCR groups (90.6% vs 83.9%, p=0.009). The outcomes were similarly observed for overall survival analysis. Conclusion: Patients with pCR after NCT showed better DFS and OS across all subtypes. Achieving pathologic complete response was a good prognostic indicator especially in young age population. Younger patients with residual disease after NCT may be candidates for additional adjuvant systemic therapy after surgery. Citation Format: Young Joo Lee, Yung Il Shin, Jisun Kim, Sae Byul Lee, Hee Jeoung Kim, Il Yong Chung, Beom Seok Ko, Jong Won Lee, Byung Ho Son, Sei-Hyun Ahn. Young age breast cancer who achieve pathologic complete response after neoadjuvant chemotherapy display excellent outcome than older age breast cancers [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-16-25.