Obese women with breast cancer have 30% worse survival than non-obese women. The cause of this survival disadvantage is currently not well understood. We postulated that this was due to relative under-dosing for body size in obese compared to non-obese women.
To compare body size-adjusted chemotherapy dose between obese and non-obese women undergoing adjuvant treatment of breast cancer.
We conducted a multi-centered retrospective audit of 712 women treated since 2000 with adjuvant chemotherapy for breast cancer. Cases were identified from the hospitals’ chemotherapy database. Subject, tumour and chemotherapy data was extracted from patient charts. Dosing was analysed by comparing expected dose based on patient body surface area to actual dose received. A multivariate analysis was performed examining dose reductions across patient and tumour characteristics.
482 women had complete data available and were eligible for inclusion. In this population 30.9% (n=149) were obese with a body mass index greater than 30kg/m2. An initial dose reduction was independently associated with obesity (OR=5.08; 95% CI 1.96 to 13.14; p=0.001) Overall in the first cycle, obese women were dosed significantly less for their body size with a median 97.9% of expected dose based on actual body size, compared to 99.6% in non-obese women (p<0.001).
Obese women now account for a large proportion of breast cancer patients. These women are relatively under-dosed for body size compared to non-obese woman. The results confirm altered treatment of obese women with doses being reduced from the initiation of treatment. This may be a contributing factor to the survival disadvantage observed in obese women, compared to non-obese women with breast cancer. Further work needs to be undertaken to ascertain the relationship between individualised dose for particular body size using concentration-outcome data.