Between 15% and 30% of patients with breast cancer will develop brain metastases over time. Brain metastases are tumor cells derived from primary breast cancer that will settle and grow in brain tissue.
At present, there appears to be an increase in the diagnosis of brain metastases because of the improved diagnostic techniques and an increase in survival of metastatic patients, secondary to the multiple new treatments available.
Not all breast cancers have an equal probability of developing these metastases; they occur most frequently in triple-negative and HER2-positive women.
The vital prognosis can vary from a few months to several years depending on certain prognostic factors, such as the cell subtype of breast cancer. The breast cancer cell subtype with the lowest survival rate is reported to be triple negative, with a mean of 3.1 months from diagnosis of metastases, 3.9 months in luminal B HER2-negative tumors, 7.1 months in luminal A tumors, and 12.1 months in HER2-enriched tumors.
There are other individual characteristics of each patient that also influence prognosis. These factors include Karnofsky Performance Status, that is, the general condition of the patient. There are patients who, despite these brain lesions, have a completely independent life and are able to carry out practically all their activities of daily living, while others are bedridden and need help carrying out their basic activities. In these latter cases, the prognosis is clearly worse. Other factors are if there are many or few brain metastases, if there is involvement of the meninges and if the disease in the other locations is controlled or not. We now have indices that assess patient prognosis by combining several of the above factors, such as the GPA index, that help professionals choose the best treatment for brain metastases.
Management of Brain Metastases
In general, treatment can be local or systemic.
Local therapy includes metastatic surgery, radiosurgery, or stereotactic radiation therapy and whole brain radiotherapy. Surgery is performed in patients with a good general condition, little brain disease and when the lesion is accessible surgically. Surgery is usually complemented by stereotactic radiation therapy to the surgical cavity or radiotherapy to the entire head, as appropriate.
In cases where surgery of the brain lesion cannot be performed, it could be treated with radiosurgery or stereotactic radiotherapy, consisting of high-dose radiotherapy in a single fraction of treatment, for a given lesion. Typically, patients with little brain disease, with very well demarcated lesions surrounded by healthy tissue, are treated using this strategy.
In cases of abundant disease, whole brain radiotherapy is indicated.
Systemic therapy involves treating the brain disease with the drugs we would use to treat any other metastases. Depending on the breast cancer subtype, certain drugs or others are used. Both oral and intravenous treatments may have trouble entering the brain parenchyma. This is due to the presence of the blood-brain barrier, which filters out substances that enter the brain parenchyma. What in principle has a protective role, in practice reduces the passage of drugs into the parenchyma, making the brain a sanctuary for tumor cells.
New drugs are currently being studied in brain disease with very good results, and they will likely be approved for the treatment of metastatic brain disease caused by breast cancer.
Management of Brain and Leptomeningeal Metastases from Breast Cancer. Pellerino A, Internò V, Mo F, Franchino F, Soffietti R, Rudà R. Int J Mol Sci. 2020 Nov 12;21(22):8534. doi: 10.3390/ijms21228534