Systemic chemotherapy in patients with brain only metastatic breast cancer: A retrospective analysis.

1093 Background: The treatment of patients with brain only metastatic breast cancer (BO-MBC) remains very challenging. There is also very limited literature informing on appropriate treatment or natural history of this entity. Systemic chemotherapy in addition to targeted therapy and/or anti-estrogen treatment is often used, but little is known if it adds to the overall or disease free survival. In this retrospective study, we examine this, as well as other factors which may be associated with increased risk of CNS or systemic recurrence in these patients. Methods: A database search at a single institution identified 178 patients with brain metastases (BM) from breast cancer out of which 45 patients had BO-MBC between 2007-2020. We collected demographic, clinical, radiographic and other treatment data. Leptomeningeal disease (LMD) was diagnosed by cerebrospinal fluid (CSF) cytology, neuroimaging, or both. We used the Brookmeyer and Crowley method. Results: The patients were followed for a median of 17.9 months; 36 out of 45 patients (80%) received local treatment for BM (surgery/radiation/both) and HER2 directed antibodies or tyrosine kinase inhibitors and/or anti-estrogen treatment, whereas 9 out of 45 patients (20%) received systemic chemotherapy in addition. There were 22 out of 45 (49%) HER2 +, 5 out of 45 (11%) HR + and 18 out of 45 (40%) triple negative breast cancer (TNBC) patients. There were 17 out of 45 patients (38%) who were deemed to have low burden of BM (defined as one to three BM and largest being ≤3 cm) whereas there were 24 out of 45 patients (53%) who had high burden of BM (defined as four or more BM or largest being > 3 cm). Conclusions: Patients with BO-MBC represent a distinct entity. Despite having better survival than patients with BM and extra CNS disease these patients have a high risk of developing LMD, CNS and systemic recurrences. The addition of chemotherapy to targeted therapy and/or anti-estrogens does not decrease the rates of systemic or CNS recurrence. The ER+ subset have a lower rate of development of systemic disease, as expected due to their relatively indolent biology. The CNS and systemic recurrence seem to be higher in patients with HER2+ cancers and counterintuitively even in those with low burden of BM; albeit these were statistically insignificant.[Table: see text]