The relationship between eGFR and capecitabine efficacy/toxicity in metastatic breast cancer

The objective of this study was to evaluate the efficacy and toxicity of capecitabine in metastatic breast cancer (mBC) according to the estimated glomerular filtration rate (eGFR). A total of 135 patients included in the final analysis were stratified into 3 categories according to baseline eGFR, i.e., eGFR <60 mL/min/1.73 m² (Group 1), eGFR 60-90 mL/min/1.73 m² (Group 2) and eGFR >90 mL/min/1.73 m² (Group 3). If a patient developed a level of toxicity that would lead to capecitabine dose reduction, this was recognized as dose-limiting toxicity (DLT). The dose was reduced due to toxicity in 95 cycles. A total of 95 DLTs were seen in 76 (56.2%) of the 135 patients. When 76 patients with DLT were evaluated according to eGFR, DLT was observed in 93.3% of those in Group 1, 72.5% of those in Group 2 and 41.3% of those in Group 3 (p < 0.001). The median time to progression (TTP) of all patients was 7.4 months. No significant difference in TTP was observed in patients stratified into 3 groups according to eGFR. When the patients were divided into two groups as DLT and without DLT, the median TTP was 8.68 months (95% CI, 7.53-9.81 months) in those with toxicity and 6.23 months (95% CI, 4.04-8.43 months) in those without toxicity (log-rank p = 0.004). We found a significant relationship between low eGFR and increased risk of DLT. Having a DLT was associated with a longer TTP. It indicates the need for more data/larger study investigating these discrepancies.