Association of Primary Tumor Volume with Survival in Patients with HER-2-positive Breast Cancer After Trastuzumab Treatment: A Retrospective Cohort Study

Background: The relationship between primary tumor volume (PTV) and overall survival (OS) in patients with human epidermal growth factor receptor 2 (HER-2)-positive breast cancer following Ttrastuzumab therapy remains controversial in the medical research community. Currently, there is insufficient evidence to definitively establish the relationship between PTV and OS; understanding this relationship is critical for healthcare and public health because it has significant implications for patient outcomes. Consequently, the PTV and its effects on OS have become the focus of extensive research. Objective: The primary objective of this study was to improve our understanding of the influence of PTV on OS and elucidate the clinical implications of this correlation. The secondary objective was to determine the optimal cutoff value for assessing the effect of PTV on OS in patients with HER-2-positive breast cancer after trastuzumab treatment. Methods: In this retrospective cohort study, we analyzed the data of 666 participants retrieved from the Dryad database. Relevant variables, including PTV, OS, lymph node status, Nottingham Histology Grading, Ki-67 expression, and age, were collected for all participants. We employed Cox regression analysis to explore the potential interaction effects to support our research objectives. Results: In total, 666 patients were identified during the follow-up period. The mean (standard deviation, SD) age of participants was 60.7 years, and all were women. The mean (SD) tumor volume was 19.9 (11.1) mm. With a mean (SD) follow-up of 82.4 (30.2) months, increasing tumor volume (per 1-mm increase) was associated with significantly worse adjusted OS (hazard ratio, 1.03; 95% confidence interval, 1.02–1.05). Conclusions: To the best of our knowledge, this extensive retrospective cohort study of patients with HER-2 positive breast cancer after trastuzumab treatment is the first to demonstrate a significant association between the PTV and a 3% increase in the risk of OS.