Normal breast size, breast hypertrophy, and gigantomastia: A proposed classification based on real-world mastectomy data.

Abstract

Female breast size varies widely, yet little scientific evidence defines what constitutes normal size and how factors such as age and body mass index (BMI) shape its variation. This study was conducted to examine the relationship between breast size, age, and BMI. In total, 1934 mastectomy specimens from consecutive patients with breast cancer and known BMI who underwent surgery between 2010 and 2022 were weighed to characterize normal breast size across different BMI categories. The associations between breast weight, patient age, and BMI were analyzed across different BMI categories. Mean breast weight and BMI demonstrated a strong linear association (R² = 0.988). BMI explained ∼60% of breast weight variation (R² = 0.588), whereas the age of the patient explained <2% (R² = 0.017). The distribution of breast weights approximated a normal distribution within BMI categories. The average weight of a single breast constitutes 0.5% of body weight in individuals with BMI of 15 kg/m², 1% in individuals with BMI of 27 kg/m², and 1.5% in patients with BMI of 38 kg/m²; an average breast weighs 1 kg in individuals with BMI of 31 kg/m². Based on the observed distributions, 95.7% of the specimens deviated by no more than two standard deviations from the BMI-adjusted mean. Breast size correlates strongly with BMI. Regardless of BMI, normal breast weight can be defined as no more than two standard deviations from the BMI-adjusted mean breast weight.