Purpose: Low rates of germline genetic testing (GGT) for breast cancer (BC) have been reported globally, with limited data from low- and middle-income countries (LMICs). In this study, we used real-world data to assess the GGT rate for BC in an LMIC and identified barriers to its use.

Methods: We analyzed 2,974 newly diagnosed patients with BC from the AMAZONA III study, the largest Brazilian multicenter, prospective BC cohort. GGT rates were determined for the entire cohort and the high-risk hereditary BC group (HR), defined by the National Comprehensive Cancer Network criteria, between 2019 and 2020. Barriers to GGT performance associated with patient characteristics and health care systems were identified using multivariable Poisson regression model. Values of P < .05 were considered significant.

Results: In the AMAZONA III cohort, 1,476 (49%) were classified as HR. Genetic counseling was recommended for 521 patients (35% of HR), and 282 (19%) underwent GGT. Notably, 97% of patients with HR treated within the public health care systems and 56% in the private system did not undergo GGT. Age, education, occupation, monthly income, availability of onsite genetic counseling, and treatment at a teaching center were factors associated with GGT uptake (P < .05). Of those tested, 50 (17%) harbored a germline pathogenic or likely pathogenic variant.

Conclusion: Only 9% of this robust Brazilian BC cohort underwent GGT, highlighting a considerable gap from the current recommendation to test all patients with BC under age 65 years. GGT is underused by patients with HR in both public and private health care systems, with those in the public system being more affected. The disparities and barriers identified emphasize the need for educational interventions and enhanced access to GGT. Prioritizing GGT is critical to improving BC outcomes in LMICs.