Impact of Body Mass Index on Outcomes After Breast Cancer Surgery: Nationwide Inpatient Database Study in Japan

Recent studies have shown better postoperative outcomes in mildly obese patients, a phenomenon called the obesity paradox. In the field of breast cancer surgery, however, previous studies have only shown an association between obesity and worse postoperative outcomes using multivariable analysis; the obesity paradox has not been investigated in patients undergoing breast cancer surgery.

We identified patients who underwent mastectomy for stage 0 to III breast cancer from July 2010 to March 2017 using a Japanese nationwide inpatient database. We used restricted cubic spline analyses to investigate potential nonlinear associations between body mass index (BMI) and outcomes (postoperative complications, 30-day readmission, duration of anesthesia, length of hospital stay, and hospitalization costs). We also performed multivariable regression analyses for the outcomes.

Among 239,108 eligible patients, 25.6% had a BMI of > 25.0 kg/m². BMI showed U-shaped associations with postoperative complications, length of stay, and hospitalization costs, and a linear association with duration of anesthesia. The proportion of postoperative complications was lowest at a BMI of around 22.0 kg/m², while the length of stay was shortest and total costs were lowest at a BMI of around 20.0 kg/m². Compared to a BMI of 22.0 kg/m², a BMI of > 30.0 kg/m² was significantly associated with greater postoperative complications, 30-day readmission, duration of anesthesia, length of stay, and hospitalization costs.

Restricted cubic spline analyses displayed U-shaped associations between BMI and in-hospital complications, length of stay, and hospitalization costs, but none of the associations showed the obesity paradox.