The radiotherapy scheme with extreme hypofractionation has gained space in clinical practice and, therefore, it is necessary to analyze the Brazilian national experience in selected patients with breast cancer, with the aim of evaluating the oncological outcomes and toxicities with the use of this treatment protocol.

All patients diagnosed with breast cancer who meet the eligibility criteria at participating centers will be included. Data will be collected from medical records at selected centers. Data collection will start from the location activation date. Data from up to 500 patients are expected to be collected at centers across Brazil.

Patients recruited for this study will be identified at participating centers. Data on clinical, demographic and socioeconomic variables will be collected, as well as data on treatments performed and outcomes.

The patient data sources will be the patients' medical records. Patients will continue to receive treatment and clinical evaluations for their illness as determined by their medical team, in accordance with the standards of care and usual clinical practice at each center. No intervention is proposed in this study.

Inclusion Criteria:

• Women over 18 years old;
• Diagnosis of breast cancer of any molecular subtype;
• Undergoing extreme hypofractionated radiotherapy (5 x 5.2Gy) postoperatively;
• Treated from December/2019 onward;
• With clinical and treatment data available in medical records.

Exclusion Criteria:

• The protocol does not provide exclusion criteria.

Women with breast cancer undergoing radiotherapy with extreme hypofractionation.