Association of HER2 status with chemotherapy burden in breast cancer: a retrospective cohort study

Human epidermal growth factor receptor 2 (HER2)-positive breast cancer is characterized by aggressive tumour biology and is routinely treated with HER2-targeted therapy in combination with chemotherapy. Although HER2 status is a key determinant of therapeutic decision-making, its association with chemotherapy treatment burden in routine clinical practice remains insufficiently characterized. The primary objective was to compare the number of documented chemotherapy sessions between HER2-positive and HER2-negative breast cancer patients; associations with clinicopathological characteristics were secondary objectives. A retrospective cohort study was conducted involving 194 women with histologically confirmed breast cancer treated at King Abdulaziz University Hospital, Jeddah, Saudi Arabia, between 2015 and 2021. Clinicopathological data, including age, HER2 status, estrogen receptor (ER) and progesterone receptor (PR) status, tumour size, histological subtype, tumour grade, lymph node involvement, and treatment characteristics, were extracted from electronic medical records. The primary outcome was the number of chemotherapy sessions administered. Comparisons between HER2-positive and HER2-negative groups were performed using the Wilcoxon rank-sum test, Chi-square test, or Fisher’s exact test, as appropriate. Among patients who received chemotherapy, HER2-positive tumours were associated with a significantly greater chemotherapy burden than HER2-negative tumours, reflected by a higher median number of chemotherapy sessions (17 vs. 12; p = 0.0015). HER2 positivity was significantly associated with patients aged 40–59 years ( p = 0.011), larger tumour size ( p = 0.050), ER-negative status ( p = 0.005), and PR-negative status ( p = 0.004). No significant associations were observed between HER2 status and tumour grade, histological subtype, lymph node involvement, treatment duration, or year of diagnosis (all p > 0.05). HER2-positive breast cancer was associated with a substantially greater chemotherapy treatment burden in this real-world cohort, consistent with current treatment strategies incorporating intensive systemic therapy for this molecular subtype. The observed associations between HER2 status and hormone receptor expression further emphasize the biological heterogeneity of breast cancer and the importance of molecular stratification in guiding individualized treatment. These findings contribute real-world evidence regarding treatment utilization and may inform future strategies aimed at optimizing therapeutic intensity while minimizing treatment burden. Not Applicable.