Abstract PS7-36: Subtype-dependent locoregional recurrence patterns in different subtypes of breast cancer: A retrospective analysis of 16,505 patients over 10 years of follow-up
Authors: Cheun Jong Ho , Lee Han-Byoel , Han Wonshink , Noh Dong-Young , Moon Hyeong-Gon 
Published: February 2021

Abstract
Background While numerous studies have consistently reported that the molecular subtypes of breast cancer are associated with different patterns of distant metastasis, the impact of molecular subtypes on the locoregional recurrence has not been thoroughly investigated. Currently, major guidelines in breast cancer recommend annual mammography for locoregional surveillance. In the present study, we investigated the patterns of locoregional recurrence in a large cohort of breast cancer patients who underwent standardized treatment at a single institution.
Methods We retrospectively reviewed the clinical records of all patients who underwent breast cancer surgery for stage I-III diseases between January 2000 and December 2018. The patients with ductal carcinoma in situ who underwent standard treatment were also included. The events were classified into ipsilateral breast cancer recurrence (IBTR), locoregional recurrence (LRR) and contralateral breast cancer (CBC). All IBTR events were included in the LRR events. The patients with initial stage IV breast cancer, with recurrence breast cancer previously treated at elsewhere, or patients with insufficient follow-up period were excluded.
Results A total of 16,505 patients were identified and included in the analysis. For all patients, the rate of IBTR, LRR, and CBC at 10 year was 2.6%, 4.9% and 1.9%, retrospectively. There was no significant association between the IHC-based molecular subtype and tumor recurrences in the 1,535 patients with ductal carcinoma in situ. For 14,970 patients with invasive disease, we observed significant differences in IBTR, LRR, and CBC between different molecular subtypes. For all events, HR-/HER2+ subtype and HR-/HER2- subtype showed worst recurrence-free survival compared to other subtypes (p&lt;0.001). However, when each event-types was separately analyzed, we observed a unique subtype-specific outcome differences according to different types of events. For IBTR, HR-/HER2- subtype showed significantly worse outcome compared to HR+ tumors (p&lt;0.001) but HR-/HER2+ subtype showed significantly higher number of events even compared to HR-/HER2- (p=0.026). For LRR, HR-/HER2+ and HR-/HER2- subtypes showed similar degree of worsening outcome compared to other subtypes (p&lt;0.001). For CBC, HR+/HER2- subtype showed significantly better outcome compared to other subtypes (p&lt;0.001). Interestingly, while the risk of development of LRR in HR+ subtypes was steady over time, the HR- subtypes showed increased risk of developing LRR during the first three years of follow-up. After that, all subtypes showed constant risk of developing LRR. In HR-/HER2+ subtype and HR-/HER- subtype, 68.2% and 75.5% of LRR events were manifested during the first three years, respectively. In contrast, HR+/HER2- and HR+/HER2+ subtypes had 43.5% and 56.5% of LRR events during the same period. In terms of CBC, all subtypes showed consistent annual risk of developing CBC during the follow-up period. The HR-/HER2- showed significantly increased risk of developing CBC compared to HR+/HER2- subtype until seven years of follow-up.
Conclusions We propose a subtype-specific locoregional and contralateral breast recurrence patterns in operable breast cancer patients by using a large cohort of breast cancer patients with sufficient long-term follow-up. These findings suggest a subtype-based tailored approach for locoregional and contralateral breast recurrences after curative treatment
Citation Format: Jong Ho Cheun, Han-Byoel Lee, Wonshink Han, Dong-Young Noh, Hyeong-Gon Moon. Subtype-dependent locoregional recurrence patterns in different subtypes of breast cancer: A retrospective analysis of 16,505 patients over 10 years of follow-up [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS7-36.