GENE PROFILING IN TUMOR SAMPLES FROM PATIENTS WITH LOCOREGIONAL BREAST CANCER

Introduction: Breast cancer is the deadliest cancer in Brazilian women; acccording to the estimate of the National Cancer Institute for the year 2021, there were 66,280 cases of breast cancer in Brazil; with an expected risk of 61 cases per 100,000 women. These data highlight the need to identify more effective prognostic biomarkers to classify the risk of recurrence and, thus, provide more personalized systemic adjuvant treatment for these women. The gene profile of primary tumors can provide important prognostic and predictive information. Although the Oncotype® DX platform is commercially available and has great prognostic value for clinic practice, its high cost to the patient (approximately US $4,000.00) makes it inaccessible to most patients with breast cancer in Brazil. Objective: To facilitate the access of the Brazilian population to more accurate, cheaper, and faster molecular tests for prognostic evaluation, we aimed to developed a specific clinical model that evaluates, through the study of the expression of the 21 genes in the Oncotype platform, their potential value for women already diagnosed with initial breast cancer. Methods: Tumor samples from 167 patients diagnosed with stage I, II, and III mammary carcinoma, who were also referred for adjuvant/neoadjuvant chemotherapy, were assessed the TGP, which was determined by analyzing the expression of Oncotype 21 genes in paraffin embedded tissue samples by quantitative multiplex RT-PCR. Results: Reactions standardized by our group are performed in multiplex, their cost is below all available tests to date (US $500.00). We observed a statistically significant correlation between the progression-free interval (PFI) and the clinical stage (p=0.000701), the TGP score (p= 0.006538), and the presence of hormone receptors in the tumor (p=0.0432). Multivariate analysis revealed that only the TGP score significantly correlated with the PFI (p= 0.029247). However, it was observed that the processing of the tumor sample has a strong influence on the result of the genetic profiling. Conclusion: The TGP is an important prognostic variable for patients with locoregional breast cancer. We suggest, however, that there is a standardization of the protocol so that reliable results are generated.