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

Takaaki Konishi, Michimasa Fujiogi, Nobuaki Michihata, Kojiro Morita, Hiroki Matsui, Kiyohide Fushimi, Masahiko Tanabe, Yasuyuki Seto, Hideo Yasunaga
Clinical Breast Cancer 2020 May 11

BACKGROUND: 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.

PATIENTS AND METHODS: 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.

RESULTS: 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.

CONCLUSION: 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.

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