RADT-15. PREOPERATIVE SINGLE FRACTION RADIOSURGERY VERSUS POSTOPERATIVE FRACTIONATED RADIOSURGERY FOR RESECTED BRAIN METASTASES: A BI-INSTITUTIONAL ANALYSIS OF SAFETY AND CLINICAL OUTCOMES

BACKGROUND

Preoperative single fraction radiosurgery (SRS) and postoperative fractionated SRS delivered over 3–5 fractions have been shown to have favorable outcomes compared to postoperative single fraction SRS for resected brain metastases. No study has directly compared these 2 treatment approaches.

METHODS

Records for patients with resected brain metastases treated with either single fraction preoperative SRS or fractionated (3-5 fractions) postoperative SRS were reviewed. Preoperative SRS was 10-20% dose reduced compared to standard and surgery generally followed within 48 hours. Eligibility criteria included solid tumor metastases, 1 brain metastasis resected, and no previous cranial RT. Fine-Gray and Cox multivariable (MVA) and propensity score matched (PSM) analyses were used.

RESULTS

A total of 330 patients (137 preoperative; 193 postoperative) were included. Median dose was 15 Gy in 1 fraction and 24 Gy in 3 fractions, respectively. In MVA, preoperative SRS was significantly associated with higher risk of cavity local recurrence (LR, hazard ratio (HR) 2.04, p=0.002) and lower risk of leptomeningeal disease (LMD, HR 0.41, p=0.05). There was no difference in adverse radiation effect (ARE) or overall survival (OS) between groups. In the PSM analysis (65 matched pairs), 1-year outcomes for preoperative vs. postoperative SRS were as follows - cavity LR: 22.9% vs. 3.1%, p< 0.001, LMD: 4.2% vs. 15.5%, p=0.04, ARE: 3.2% vs. 7.9%, p=0.73, composite endpoint (cavity LR, symptomatic ARE, or LMD): 27.6% vs. 20.1%, p=0.33, OS: 56.3% vs. 62.3%, p=0.8.

CONCLUSIONS

Preoperative single fraction SRS and postoperative fractionated (3-5 fractions) SRS demonstrate distinct patterns of failure. Compared to postoperative SRS, preoperative SRS was associated with increased risk of cavity LR and lower risk of LMD in both multivariable and PSM analyses. There was no difference in risk of ARE or OS. Methods to reduce preoperative SRS cavity LR, such as with higher dose fractionated regimens, should be considered.

LPTO-06. A NOVEL BRAIN-PERMEANT CHEMOTHERAPEUTIC AGENT FOR THE TREATMENT OF BREAST CANCER LEPTOMENINGEAL METASTASIS

Leptomeningeal metastasis (LM), a spread of cancer to the cerebrospinal fluid and meninges, is universally and rapidly fatal due to poor detection and no effective treatment. Breast cancers account for a majority of LMs from solid tumors, with triple-negative breast cancers (TNBCs) having the highest propensity to metastasize to LM. The treatment of LM is challenged by poor drug penetration into CNS and high neurotoxicity. Therefore, there is an urgent need for new modalities and targeted therapies able to overcome the limitations of current treatment options. Quadriga has discovered a novel, brain-permeant chemotherapeutic agent that is currently in development as a potential treatment for glioblastoma (GBM). The compound is active in suppressing the growth of GBM tumor cell lines implanted into the brain. Radiolabel distribution studies have shown significant tumor accumulation in intracranial brain tumors while sparing the adjacent normal brain tissue. Recently, we have demonstrated dose-dependent in vitro and in vivo anti-tumor activity with various breast cancer cell lines including the human TNBC cell line MDA-MB-231. To evaluate the in vivo antitumor activity of the compound on LM, we used the mouse model of LM based on the internal carotid injection of luciferase-expressing MDA-MB-231-BR3 cells. Once the bioluminescence signal intensity from the metastatic spread reached (0.2 - 0.5) x 10⁶ photons/sec, mice were dosed i.p. twice a week with either 4 or 8 mg/kg for nine weeks. Tumor growth was monitored by bioluminescence. The compound was well tolerated and caused a significant delay in metastatic growth resulting in significant extension of survival. Tumors regressed completely in ~ 28 % of treated animals. Given that current treatments for LM are palliative with only few studies reporting a survival benefit, Quadriga’s new agent could be effective as a therapeutic for both primary and metastatic brain tumors such as LM. REF: https://onlinelibrary.wiley.com/doi/full/10.1002/pro6.43