Objective: Protein HER2 identifies a more aggressive subtype of breast cancer. For this type of tumor, currently there are specific treatments (trastuzumab and lapatinib), which, if used in early phase of the disease can render a higher chance of cure and survival to the patients (the HERA study showed that the use of Herceptin after a standard chemotherapy in adjuvant tumors has reduced by 46% the risk of a tumor to return). The study objective is to assess the performance of the diagnostic tests of this protein for Brazilian patients with breast cancer. Methods: A diary study with 220 Brazilian clinical oncologists was used; in the end of the study, a total of 3994 patients with breast cancer were followed up. Results: Fifty-eight percent of the patients found were in the public market, and 42% were from the private market. We also have that 64% of the patients have early tumors (adjuvant or neoadjuvant), and 36% have metastatic tumors. The HER2 test is performed in 80% of the patients in the private market, with only 36% of the patients of the public market being tested. The test performance rate has little correlation with the disease phase (P value = 0.81); however, there is some correlation of the performance of this test with the patient's age (P value = 0.3). Physicians from several Brazilian states have different behavior while performing this exam (P value = 6^162) Conclusion: We verified that few patients of the public market (36%) perform this test comparing with the private market (80%). We also verified great differences in the performance of it in the different regions of the country. An increased performance rate of this exam would increase the chances of survival and cure for the patients, since it allows the use of specific treatments for positive HER2 tumors.