Brain metastases are the most common intracranial malignant tumor in adults and are a cause of significant morbidity and mortality for cancer patients. Large brain metastases, defined as tumors with a maximum dimension >2 cm, present a unique clinical challenge for the delivery of stereotactic radiosurgery (SRS) as patients often present with neurologic symptoms that require expeditious treatment that must also be balanced against the potential consequences of surgery and radiation therapy—namely, leptomeningeal disease (LMD) and radionecrosis (RN). Hypofractionated stereotactic radiotherapy (HSRT) and pre-operative SRS have emerged as novel treatment techniques to help improve local control rates and reduce rates of RN and LMD for this patient population commonly managed with post-operative SRS. Recent literature suggests that pre-operative SRS can potentially half the risk of LMD compared to post-operative SRS and that HSRT can improve risk of RN to less than 10% while improving local control when meeting the appropriate goals for biologically effective dose (BED) and dose-volume constraints. We recommend a 3- or 5-fraction regimen in lieu of SRS delivering 15 Gy or less for large metastases or resection cavities. We provide a table comparing the BED of commonly used SRS and HSRT regimens, and provide an algorithm to help guide the management of these challenging clinical scenarios.

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e17587 Background: Survival outcomes remain poor in salivary gland malignancies (SGMs) with multiple poor prognostic factors despite adjuvant radiotherapy. We examined prognostic factors that portended poor survival in resected SGMs to determine possible indications for adjuvant chemoradiotherapy. Methods:Patients who underwent curative resection with or without adjuvant radiotherapy between 2002 and 2014 were identified and retrospective chart review was performed. Bivariate analysis was performed on continuous variables using Analysis of Variance. Chi-Square analysis and Fishers Exact Tests were performed on categorical variables. To evaluate the overall survival (OS) and disease-free survival (DFS), Kaplan-Meier curves and log-rank tests of homogeneity were used. Results: Overall, 99 patients met inclusion criteria. Median follow-up time was 46.8 months. Univariate analysis revealed male sex, smoking history ≥ 10 pack-years, high grade, stage III-IVB, squamous cell histology, and perineural invasion significantly impacted OS and DFS. High-risk histopathology significantly impacted DFS and trended towards poor OS. Positive resection margins trended towards significantly impacting DFS. Multivariate analysis revealed only male sex and perineural invasion significantly impacted OS and DFS. Conclusions: Survival outcomes remain poor for patients with high-grade, late-stage tumors with perineural invasion. Specifically, perineural invasion is a poor prognostic factor regardless of age, histology, stage, and grade. Males and patients with a smoking history ≥ 10 pack-years have worse survival outcomes with male sex being a more influential prognostic factor. Notably, this is the first study to quantify patient’s smoking history in malignant salivary gland tumors and assess the impact of pack-year smoking history on survival outcomes. Given our observed trend, positive resection margins would likely become significant influencer of DFS with larger sample size and longer follow up. Adjuvant chemoradiotherapy should be evaluated in patients with the above-mentioned characteristics.

Adjuvant chemoradiotherapy should be considered for patients with tumors with perineural invasion, especially in males with high-risk histopathology or high-grade, late-stage disease. To our knowledge, this is the first study to assess the impact of pack-year smoking history on survival outcomes.

Gastrointestinal stromal tumor (GIST) is an uncommon mesenchymal tumor, and has been shown to be associated with synchronous or metachronous second malignancies. Rare cases of coincident GIST and non-Hodgkin lymphomas (NHL) have been reported previously. Here, we report two cases of GIST and coincident primary breast lymphoma, an uncommon subtype of extranodal NHL. We propose that the exceedingly low likelihood of both these cancers occurring in these two patients by chance warrants examination for possible common oncogenic pathways in these lesions, possibly involving shared anti-apoptotic mechanisms. Further research is vital to elucidate common oncogenic pathways between such rare lesions.