Background/Aims: This cross-sectional study investigates body composition and strength in female breast cancer survivors, focusing on the effects of radical mastectomy and the presence of upper extremity lymphoedema. The main objective was to understand body composition, volumetry, and strength, as well as response to strength training in female breast cancer survivors. Methods: Twenty-three women (aged 42–74 years old) with radical mastectomy in the last five years were assessed by measuring body composition (weight, water percentage, fat, muscle, and lean mass), maximal strength, perimeters, and brachial volumes. Participants completed a 10-week strength training program of moderate intensity with 20 training sessions. No significant differences were found between the affected/healthy hemispheres in terms of composition, perimeters, and volumetrics. However, 11 women were found to have lymphoedema (47.8%). No statistically significant differences were found between hemibodies after the intervention, although improvements were obtained in pectoral strength and manual grip, as well as in muscle mass and lean mass [p = 0.002 each]. Cases with lymphoedema were reduced to 5 (21.73%). Conclusions: While strength training is shown to benefit body composition, strength, and the incidence of lymphoedema in mastectomized women, further scientific evidence is needed with larger controlled trials and follow-up studies to validate these findings, as well as the impact on the quality of life of these survivors.