After a breast cancer diagnosis, patients are at high risk of reducing their physical activity and gaining weight. Lack of physical activity and weight gain are known negative but modifiable prognostic factors. An observational study of a 3-month adapted physical activity (APA) program was performed to assess its effectiveness in improving physical activity level and reducing risk factors related to health during or after breast cancer treatments. Height, weight, and waist circumference (WC) were measured at the beginning and end of the 26-session program. Body mass index (BMI) and WC to height ratio (WHtR) were calculated. Physical activity profile, aerobic capacity, and usual average daily energy expenditure were estimated. Median values were compared using nonparametric tests. Sixty-one (61) voluntary breast cancer patients attended 80% of the sessions. At baseline, median (minimum-maximum) BMI was 23.3 (16.1-36.8) kg.m(-2) and WC and WHtR showed metabolic risks. After 3 months, anthropometric data remained stable. Moderate physical activity significantly improved (+13 min/day) and sedentary tended to decrease (-18 min/day). A 3-month APA program allows patients to limit risk factors related to health such as physical inactivity and metabolic risks. This study reinforces the need to promote physical activity as early as possible in cancer patients' care.