Weight gain during chemotherapy is frequently reported in breast cancer patients and adversely impacts survival and quality of life. However, weight change over the long term and its determinants in breast cancer patients who received chemotherapy remain unclear. This study aimed to characterize weight change over 13 years among French breast cancer patients diagnosed with early-stage breast cancer who received adjuvant chemotherapy.

We examined weight change over 13 years in a cohort of 267 early breast cancer patients diagnosed between 2004 and 2006 and treated with adjuvant chemotherapy. Yearly weight measures were obtained from medical records, or from questionnaires when not available from medical records. We compared weight at each time using analysis of variance for repeated data based on mixed-effect models, and examined clinical and individual factors as potential determinants of weight change over the study period.

More than one third of women experienced weight gain > 5% of their initial body weight following initiation of adjuvant chemotherapy (34.6%, 36.0%, 41.6%, and 37.4% at years 1, 5, 10, 13, respectively). A statistically significant weight gain occurred during the first year after initiation of chemotherapy (estimated mean gain: 1.80 kg; 95% confidence interval (0.52–3.1) kg) and was maintained for up to 13 years (P-value for overall effect of time on weight < 0.001). This weight gain was observed only for women with an initial BMI < 25 kg/m². Type of chemotherapy, use of hormone therapy, age at inclusion, menopausal status, or physical activity level at initial visit did not show statistically significant association with weight change.

These results emphasize the need to improve our understanding of weight change and its determinants and to develop effective intervention strategies to prevent weight gain for breast cancer patients during the first year of treatment.