Discordance in biomarker expression between primary breast cancers and loco-regional recurrences: a comprehensive analysis of 112 cases.

Background: Breast cancer is a complex disease encompassing multiple phenotypic and genetic subtypes. The biomarker status of primary and recurrent lesions may be dissimilar, and changes in biomarker status may inform clinical decision-making. The expression of biomarkers between primary breast cancers and loco-regional recurrences lacked large sample studies. This study aimed to investigate the discordance in the status of specific biomarkers between primary breast cancers and loco-regional recurrences, while also exploring the associated clinical and pathological characteristics of the affected patients.

Methods: A retrospective review was conducted on the medical records of 112 female patients with a confirmed pathological diagnosis of breast cancer who experienced loco-regional recurrence between July 2005 and March 2018 at Peking Union Medical College Hospital. Comprehensive data regarding primary and recurrent tumor characteristics, surgical interventions, history of systemic therapy, presence and management of loco-regional recurrences, as well as disease-free survival (DFS) and overall survival (OS), were systematically recorded and subsequently subjected to comparative analysis.

Results: The study revealed disparities in the expression of individual biomarkers between primary breast cancers and loco-regional recurrences, with discordance rates exhibiting variation across breast cancer subtypes. Specifically, the overall discordance rates were as follows: 9.8% for estrogen receptor (ER) expression, 15.2% for PR expression, 7.6% for human epidermal growth factor receptor-2 (HER2) expression, and 20.6% for the Ki-67 index (21 out of 102 cases). Luminal A tumors exhibited the highest discordance rate at 81.8%, while triple negative (TN) tumors displayed the lowest at 9.1%. Furthermore, a statistically significant association was identified between DFS and the subtype of primary breast cancer (P=0.002).

Conclusions: The study shows that there exists discordance in the expression of individual biomarkers between primary breast cancers and loco-regional recurrences. The discordance rate was found to be highest among luminal A tumors and lowest for TN tumors. Additionally, patients with HER2 and TN primary breast tumors exhibited the shortest DFS. Based on these findings, the study recommends the implementation of biomarker testing for recurrent breast cancers as a valuable strategy to inform and guide decisions regarding the selection of rescue chemotherapy, endocrine therapy, and targeted therapy.