Characteristics and treatment outcomes in HER2 positive and triple negative breast cancer patients: the impact of obesity on women with hormone-negative breast cancer

Introduction: Breast cancer (BC) is a leading cause of cancer-related morbidity and mortality in women globally. The HER2+ and triple-negative (TN) subtypes exhibit distinct biological behaviors and treatment outcomes. With rising obesity rates, it is crucial to understand how obesity affects treatment responses in these hormone-negative subtypes to improve patient management.

Objective: This study aims to compare demographic characteristics, tumor features, and treatment outcomes between HER2+ and TNBC patients, focusing on the impact of obesity on treatment efficacy.

Methods: This retrospective analysis included women with histological diagnoses of BC treated at a SUS hospital in São Paulo from June 2016 to June 2023. Participants aged 18 or older, diagnosed with TNBC or HER2+ who received neoadjuvant chemotherapy were included. Data were collected from electronic medical records with approval from the Research Ethics Committee. A total of 76 HER2+ and 160 TN patients were included. Clinical and histopathological data included menopausal status, age, ethnicity, tobacco and alcohol consumption, number of births, and body mass index (BMI ≥ 30). The analysis assessed surgery type (mastectomy vs. quadrantectomy), radiotherapy (yes/no), and chemotherapy response (complete pathologic response [PCR] vs. residual disease), along with tumor stage, nodal stage, presence of metastases, histological type, and Ki67 expression.

Results: The HER2+ group demonstrated a higher PCR rate of 44.7% compared to 33.1% in the TN group (p = 0.0075). Mastectomy was performed in 57.9% of HER2+ patients and 45.6% of TN patients (p = 0.6288). Among obese patients, those with HER2+ (n = 27) had a higher mastectomy rate (63.0%) than TN patients (n = 54) at 40.7% (p = 0.0979). Significant differences in radiotherapy were noted, with 74.1% of obese HER2+ receiving it versus 96.3% of TN patients (p = 0.0053). PCR in obese HER2+ patients was 66.7%, higher than 35.2% in obese TN patients (p = 0.0096).

Conclusion: This study reveals significant differences in treatment responses and surgical decisions between HER2+ and TNBC patients, especially regarding obesity. Understanding the impact of obesity on treatment outcomes in these hormone-negative subtypes is vital for tailoring individualized treatment plans. Future research is needed to explore the relationship between obesity and treatment efficacy in these BC subtypes.

Corresponding author: Grazielle Morais Tavares (e-mail: graziellemoraist@gmail.com).