Identification of Risk Factors for Brain Recurrence in Patients With HER2-positive Localised Breast Cancer

HER2 gene amplification, detected in 20% to 30% of breast cancers, was a poor prognostic factor before the advent of anti-HER2 therapies. In the early 2000s, trastuzumab revolutionised the management of patients with HER2-positive (HER2+) breast cancer in the metastatic and localised stages of the disease. At the time of diagnosis of metastatic disease, 7-11% of patients have brain metastases, with (70% of cases) or without symptoms (30% of cases). In the absence of brain metastases, 30% to 50% of patients will develop brain metastases within the first two years of treatment, depending on whether the disease is hormone receptor positive (HR+) or negative (HR-). The presence of brain metastases is the most important prognostic factor. The neurological symptoms caused by the presence of these lesions, but also by the local treatments offered, affect patients' quality of life, although improvements in surgical and radiotherapy techniques have significantly reduced the need for particularly toxic whole brain radiotherapy. International guidelines do not recommend systematic brain MRI in the absence of neurological symptoms, either in the adjuvant or metastatic stages of this disease. However, there may be a role for more systematic and earlier screening for cerebral recurrence, as single cerebral recurrences without extracranial involvement are common and the new anti-HER2 agents (i.e. tucatinib, an anti-HER2 tyrosine kinase inhibitor, and T-Dxd) have shown significant objective response rates in cerebral metastases. To date, no clinical or histological prognostic factor (proliferation index, HR expression, etc.) has been used to identify a population of patients at high risk of cerebral relapse, allowing monitoring and treatment to be personalised. New tools for these indications would significantly modify our clinical practice, allowing the identification of a subpopulation at high risk of cerebral recurrence, suitable for increased monitoring and therapeutic adjustment.