<p><strong>Introduction</strong>: breast cancer (BC) is the most common tumor and the leading cause of cancer-related death among the female population<br />worldwide. Polymorphisms genetics of ABCB1 gene contributed to breast cancer susceptibility and interindividual differences in<br />chemotherapy response. <strong>Objectives</strong>: to evaluate the association between the ABCB1 C3435T gene polymorphism (SNPs) with the<br />response to neoadjuvant chemotherapy in women with breast cancer. <strong>Methodology</strong>: this study included 32 female patients who<br />received neoadjuvant chemotherapy. The polymorphisms were genotyped through real-time allele-specific polymerase chain reaction<br />(PCR). The statistical analysis was performed using the Fisher’s exact test or Pearson’s chi-square test in the Statistical Package for<br />Social Sciences (SPSS) version 20.0 software. <strong>Results</strong>: the genotypes found for the C3435T polymorphism were in Hardy-Weinberg<br />equilibrium and their genotypic distributions were CC= 10 (31.1%), CT= 14 (43.8%), and TT= 08 (25.0%) with χ2: 0.86 and p-value &gt;<br />0.05. Allele frequencies were C = 0.54 and T = 0.46. There were no significant statistical differences between genotypes considering the<br />response to neoadjuvant chemotherapy and immunohistochemistry; the presence of the T allele was associated with worsen axillary<br />status response to neoadjuvant chemotherapy. <strong>Conclusion</strong>: no definite association between the presence of C3435T polymorphism<br />and the response to neoadjuvant chemotherapy was observed. Further studies in Brazil involving larger samples will contribute to<br />validating the results of this study.</p>