Background and importance The response and the toxicity profile associated with capecitabine treatment shows great interindividual variability. The study of genetic polymorphisms of genes involved in the metabolism of capecitabine could help to predict the response and toxicity to breast cancer treatment.

Aim and objectives To evaluate both the response and toxicity of patients with breast cancer treated with capecitabine, as well as its relation to some genetic polymorphisms of genes involved in the metabolism of capecitabine (UMPS, TYMP and UPB1).

Material and methods A prospective observational study was conducted during 2021 in a third-level hospital. The study had been approved by the Ethics and Clinical Research Committee of the Hospital with the prior informed consent of the patients for their inclusion in the study. Clinical and demographic characteristics were obtained by reviewing the clinical history of the patients. The response was evaluated according to the RECIST 1.1 criteria and toxicities were categorised according to version 5.0 of the CTCAE. A DNA extraction was performed from swabs with saliva samples using a QIAamp DNA Mini Kit. Genetic markers were analysed via OpenArray by QuantStudio 12K Flex System using the ‘TaqMan PGx Express’ array. The relation between demographic and clinical variables and polymorphisms with response and toxicity to treatment with capecitabine were studied using bivariate analysis with R software 4.1.1 version.

Results 63 patients were treated in 2021. The evaluation of the response (n=38) resulted in complete response: 13.16% (n=5), partial response: 10.53% (n=4), stable disease: 10.53% (n=4) and progessive disease: 65.79% (n=25). An association was observed between the nulliparity (p=0.037, OR 7.2, IC95% 0.96 to 67.19) of the patients and the response to capecitabine, as well as between estrogen (p=0.024, OR 4.11, IC95% 1.15 to 15.22) and progesterone (p=0.006, OR 5.71, IC95% 1.62 to 23.84) receptors with the appearance of toxicity after treatment. No association was found between any of the studied polymorphisms with response or toxicity to capecitabine therapy.

Conclusion and relevance The results suggest that there is no relevant relation between the genetic variants analysed with the response and toxicity to capecitabine therapy. However, this result partly resembles that reflected by other studies. A larger study with a bigger patient cohort is required in order to obtain meaningful results.

References and/or acknowledgements None

Conflict of interest No conflict of interest