Impact of body mass index on outcomes following breast cancer surgery: a nationwide inpatient database study in Japan

Abstract Background Recent studies have shown better postoperative outcomes in mildly obese patients, described as 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. Materials and Methods We identified patients who underwent mastectomy for stage 0–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 the 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. Results Among 239,108 eligible patients, 25.6% had a BMI of \u003e25.0 kg/m2. The BMI showed U-shaped associations with postoperative complications, length of stay, and hospitalization costs and a linear association with the 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 with a BMI of 22.0 kg/m2, a BMI of \u003e30.0 kg/m2 was significantly associated with greater postoperative complications, 30-day readmission, duration of anesthesia, length of stay, and hospitalization costs. Conclusions Restricted cubic spline analyses displayed U-shaped associations between the BMI and in-hospital complications, length of stay, and hospitalization costs, but none of the associations showed the obesity paradox.