Recurrence dynamics of breast cancer according to baseline body mass index.

Background: In cancer follow-up, in addition to the evaluation of survival probabilities, there is a fundamental need of assessing recurrence dynamics for optimal disease management. Although the time-dependent effect of the oestrogen receptor (ER) status of the tumour has already been described, so far no factor has proven to disentangle the multi-peak behaviour observed for breast cancer recurrences. Here, we aimed at investigating whether adiposity at diagnosis, reflected by increased patient's body mass index (BMI), could be associated with breast cancer recurrence patterns over time after primary cancer therapy.

Methods: We retrieved BMI from 734 of 777 patients with node-positive breast cancer from a phase III randomised clinical trial, which compared different chemotherapy regimens and had a median follow-up of 15.4 years. Cumulative incidence estimation as well as piecewise exponential models were carried out to estimate the distant recurrence dynamics, in all patients, as well as in subgroups based on the ER status, with the ER-positive group being further split according to the menopausal status.

Results: In patients with ER-negative breast cancer, time-dependent analyses revealed that the hazard of late relapses could mainly be attributed to the overweight and obese patients. Within the subgroup of premenopausal patients with ER-positive tumours, obesity was associated with an early high narrow peak of distant recurrences followed by another main peak after 5 years of follow-up. The risk for overweight patients was intermediate between obese and normal-weight patients. In the postmenopausal subgroup of patients with ER-positive tumours, the distant recurrence rate was significantly more elevated in the overweight patients compared to the other BMI categories, and a second late peak of recurrences was also observed for the obese patients.

Conclusion: These results demonstrate that the patient's BMI at diagnosis is associated with cancer recurrence dynamics. Patient adiposity should therefore be central to the exploration of late adjuvant treatment modalities.