Purpose: Breast cancer patients with higher body mass index (BMI) experience worsened outcomes, though a knowledge gap remains regarding whether treatment differs by BMI. This study examined how BMI was associated with breast cancer treatment among Iowans.
Methods: Iowa Cancer Registry data were linked with state driver's license data to calculate BMI. Among those with stage I-III cancers, we assessed differences in breast cancer surgery (BCS), reconstruction, chemotherapy, hormone therapy, and radiation therapy between BMI categories using logistic regression models. We restricted analyses of reconstruction to individuals who received surgery, and hormone therapy to hormone receptor-positive (HR+) patients. We used multinomial models to assess the type of BCS received.
Results: Nearly all of the 18,115 included patients received surgery (97%), 63% received chemotherapy, 79% of HR+ patients received hormone therapy, and 63% received radiation therapy. Patients with higher BMI had decreased odds for reconstruction (BMI 25.0-29.9 kg/m2 aOR = 0.81, 95% CI: 0.71, 0.93; BMI 30.0-34.9 kg/m2 aOR = 0.62, 95% CI: 0.51, 0.74; BMI 35.0+ kg/m2 aOR = 0.44, 95% CI: 0.34, 0.57), and, among patients with HR+, increased odds of hormone therapy (BMI 25.0-29.9 kg/m2 aOR = 1.14, 95% CI: 1.03, 1.26; BMI 30.0-34.9 kg/m2 aOR = 1.15, 95% CI: 1.01, 1.30; BMI 35.0+ kg/m2 aOR = 1.22, 95% CI: 1.04, 1.42). Patients with higher BMI were more likely to receive lumpectomy than unilateral/bilateral mastectomy.
Discussion: These findings suggest breast cancer treatment differences exist for patients with higher BMI. Future research is warranted to understand mechanisms behind differences, both to ensure breast cancer patients with higher BMIs receive adequate and appropriate cancer care and to understand whether treatment differences contribute to observed survival differences.
Keywords: body mass index; breast cancer; treatment.
© 2026 The Author(s). Cancer Medicine published by John Wiley & Sons Ltd.