CLRM-20 IDENTIFYING RISK FACTORS AND ANALYZING SURVIVAL FOLLOWING PACHYMENINGEAL FAILURE

OBJECTIVE: Neurosurgery (NS) is an essential modality for large brain metastases (BM). As an adjuvant treatment, stereotactic radiosurgery (SRS) reduces neurocognitive toxicity without affecting post-treatment overall survival (OS) compared to whole brain radiation therapy. Pachymeningeal failure (PMF) beyond the SRS field is a relatively newly described entity, distinct from classical leptomeningeal failure (LMF), and unique to postoperative patients treated with adjuvant SRS. We sought to identify risk factors for PMF in patients treated with NS+SRS. METHODS: We reviewed a prospective registry (2009 to 2020) and identified all patients treated with NS+SRS. Clinical, radiological, pathological and treatment factors were analyzed. PMF incidence was evaluated using a competing risks model and differences between cohorts were measured using the Fine-Gray method. RESULTS: 144 Patients were identified. Median age was 62 (23-90). PMF occurred in 22.2% (32/144) patients). Univariate analysis indicated female gender (HR 2.65, p=0.013), higher GPA status (HR 2.4, p<0.001), absence of prior radiation therapy (HR N/A, p=0.018), controlled extracranial disease (CED) (HR 3.46, p=0.0038), and contact with the pia/dura (HR 3.30, p=0.0053) as risk factors for PMF. Piecemeal (vs En-bloc) resection also trended towards correlation (HR 2.07, p=0.054). Multivariate Analysis identified contact with pia/dura (HR 3.51, p=0.0053), piecemeal resection (HR 2.38, p=0.027), and CED (HR 3.97, p=0.0016) as significant correlates to PMF. PMF correlated with reduced OS (HR 2.90, p<0.001) but was improved compared to patients who developed LMF (HR 10.15, p= p<0.001). CONCLUSIONS: PMF is an underrecognized phenomenon that correlates with pre-operative pia/dura contact and piecemeal resection in patients treated with NS+SRS for BM. While less morbid than LMF, it is a critical event that deserves increased vigilance and analysis.