Prognostic impact of body mass index on metastatic HER2-positive breast cancer survival

Background. The association between body mass index and prognosis in patients with HER2-positive metastatic breast cancer (mBC) is unclear. Purpose – the first purpose of our study was to determine whether BMI is an independent prognostic factor for progression-free survival (PFS) and overall survival (OS) in HER2-positive mBC patients. The second objective was to assess the mutual impact of baseline clinicopathological characteristics on survival outcomes. Materials and Methods. The study group included patients treated at the Sumy Regional Clinical Oncology Center. We considered the underweight patients if their BMI was <18.5 kg/m2, normal weight 18.5–24.9 kg/m2, overweight 25.0–29.9 kg/m2, and obese ≥ 30 kg/m2. The following formula was used for calculations: weight/height2 (kilograms/meter2). Information about the height, weight, and other clinicopathological characteristics of the patient at the time of the start of drug therapy was taken from the primary medical documentation. Pearson’s test and Chi2 test for categorical variables were used to compare baseline clinicopathological characteristics in groups with normal, overweight, and obesity. The Kaplan-Meier method was used to establish the medians of PFS and OS. Cox regression analysis assessed the mutual impact on the survival of various clinicopathological characteristics. The statistical significance threshold was considered P ≤0.05. Results. Seventy-eight patients with HER2-positive mBC were enrolled and categorized according to their BMI in normal weight, overweight, and obese groups. BMI had a different impact on PFS and OS. Median PFS was 14.9, 11.9, and 14.2 months for normal-weight, overweight, and obese patients, respectively. There is no statistically significant difference in PFS between groups (Р = 0.110). Multivariable regression analysis confirmed no impact of BMI on PFS. Nevertheless, metastases in bones and kidneys and the nuclear grade were statistically significant determinants of PFS. Median OS was 26.4, 28.8, and 37.9 months for normal-weight, overweight, and obese patients, respectively. BMI, kidney metastases, and nuclear grade were prognostically significant determinants of OS. Conclusions. BMI is an independent prognostic factor of OS in patients with HER2-positive mBC. Obesity is associated with better OS but does not impact PFS. Metastases in bones and kidneys and the nuclear grade can predict survival outcomes.