Genomic profile in Mexican women with early-stage breast cancer using Mammaprint+Blueprint assay: A retrospective study.

e12541 Background: Genomic assays have facilitated the decision-making of using chemotherapy and hormone therapy when incorporated into the care of patients with early-stage breast cancer. Mammaprint+Blueprint have been validated as a prognostic tool in cohorts around the world. However, to date, there hasn’t been a study that addresses the use of these assays on a large Mexican population and the description of clinical characteristics associated with genomic risk. Methods: We conducted a multicenter, retrospective, descriptive study from 2012 to 2023, including women who underwent surgery, aged ≥ 18 years with tumor size less than 5 cm, hormone receptor-positive evaluated through immunochemistry (IHC), 0 to 1-3 positive lymph nodes, in early stages (I-II), who underwent the Mammaprint+Blueprint at 20 institutions in Mexico. The primary goal was to describe the clinical and genomic characteristics of these patients and calculate the discordance rate between clinical risk and genomic risk. Results: This study included 1,673 patients, with a mean age of 57 ± 11 years. Of these, 649 (39%) were classified as high-risk, and 1,024 (61%) as low-risk through MammaPrint. A discordance rate of 49% was observed in the initially clinically classified high-risk group, which was reclassified as genomic low-risk through MammaPrint. On the other hand, 33% of patients in the clinically low-risk group were reclassified as genomic high-risk. The most common molecular subtype identified through Blueprint was Luminal A (61%), and the most prevalent histologic type was ductal (79%). The predominant tumor size stage was T1 (70%), with the majority presenting with no infiltrating lymph nodes at the testing time (N0, 88%). The most common tumor grade was 2 (65%) and the proliferation rate, assessed through Ki-67, was ≥ 20% in 43% of the patients. Conclusions: Our study showed a high rate of discordance between clinical and genomic risk, a rate of 49% between clinical high-risk and genomic high-risk patients, highlighting the importance of these assays in the decision-making of breast cancer patients. This represents the first cohort to evaluate MammaPrint+BluePrint in a Latin American population. A noteworthy result was identifying a significant proportion of our cohort as low-risk through genomic assay, sparing them from the toxic effects and expenses associated with chemotherapy. Using the combined insights from MammaPrint+BluePrint along with clinical factors provides a more complete basis for predicting prognosis and benefit from specific treatments. Finally, these assays emerge as a valuable tool, particularly in middle-income countries, offering a means to improve the accurate allocation of resources in the care of their population. Due to the retrospective nature of our study, its limitations are being addressed prospectively to evaluate survival rates, distant metastasis, and recurrent cancer.