Background obesity and sedentary lifestyle have been shown to negatively affect survival
in breast cancer (BC). The purpose of this study was to test the efficacy of a lifestyle intervention on
body mass index (BMI) and physical activity (PA) levels among BC survivors in Modena, Italy, in
order to show an outcome improvement in obese and overweight patients. Methods: This study is
a single-arm experimental design, conducted between November 2009 and May 2016 on 430 women
affected by BC. Weight, BMI, and PA were assessed at baseline, at 12 months, and at the end of the
study. Survival curves were estimated among normal, overweight, and obese patients. Results:
Mean BMI decreased from baseline to the end of the study was equal to 2.9% (p = 0.065) in
overweight patients and 3.3% in obese patients (p = 0.048). Mean PA increase from baseline to the
end of the study was equal to 125% (p < 0.001) in normal patients, 200% (p < 0.001) in overweight
patients and 100% (p < 0.001) in obese patients. After 70 months of follow-up, the 5-year overall
survival (OS) rate was 96%, 96%, and 93%, respectively in normal, obese, and overweight patients.
Overweight patients had significantly worse OS than normal ones (HR = 3.69, 95%CI = 1.82–4.53 p =
0.027) whereas no statistically significant differences were seen between obese and normal patients
(HR 2.45, 95%CI = 0.68–8.78, p = 0.169). Conclusions: A lifestyle intervention can lead to clinically
meaningful weight loss and increase PA in patients with BC. These results could contribute to
improving the OS in obese patients compared to overweight ones.