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e21080 Background: A 31-GEP test is predictive of metastasis in cutaneous melanoma. We hypothesized that GEP testing would “upgrade” surveillance to routine imaging in at least 16% of stage IB/IIA patients, similar to the upgrade rate from sentinel node biopsy. Methods: A GEP score was obtained for consecutive patients with Stage IB/IIA melanoma treated between 6/2014-6/2016. A retrospective review of a prospectively collected database was performed. Results: 67 patients with Stage IB/IIA melanoma met inclusion criteria. In four cases, a GEP result was not available. Of the 63 tested cases, 68% were Stage IB (N = 43), and 32% were Stage IIA (N = 20). A high-risk result was seen in 12% of stage IB (5/43) and 42% of stage IIA (8/19) patients. Insurance denied coverage of scans in 1/13 patients with a high-risk GEP result. The remaining 12 Stage IB/IIA patients with high-risk scores were “upgraded” to high-intensity surveillance. With a median follow-up of 14 months, 1/13 patients with a high-risk GEP result developed distant metastases 21 months after diagnosis of a Stage IIA melanoma. Conclusions: Results from this retrospective single institution study show that GEP testing altered patient management in 19% of Stage IB/IIA patients. Early detection in 1/13 patients with high-risk scores in this series supports further investigation into stratifying traditionally low-risk patients by GEP testing.

e19062 Background: Sentinel lymph node biopsy (SLNB) is the standard method for staging cutaneous melanoma and involves identifying the first node(s) draining a tumor, by detecting an intradermally-injected radioactive colloid tracer. Intra-operatively the sentinel node(s) are identified with a hand-held gamma probe. Pre-operative lymphoscintigraphy is obtained to identify draining lymph node basins, but requires coordinating schedules between nuclear medicine and the operating room. A pilot study utilizing Mobile Gamma Camera (MGC) devices in conjunction with conventional lymphoscintigraphy for intraoperative sentinel node localization provided clinical benefit in 20% of patients. However, utilizing MGC devices to localize lymph node basins at the time of surgery independent of conventional lymphoscintigraphy with a fixed gamma camera (FGC) has not been adequately studied. Here, we present the results of a clinical trial utilizing MGC devices to localize lymph node basins in a manner blinded to the FGC images in order to compare the modalities directly. Methods: In 2011-12 18 patients underwent Tc99 sulfur colloid lymphoscintigraphy, and MGC survey immediately pre-operative by the study surgeon. The study surgeon established an operative plan using the MGC survey, while blinded to lymphoscintigraphy results. SLNB was then performed with use of a gamma probe and intra-operative MGC imaging. Results: 22 lymph node basins were detected in 18 imaged patients by lymphoscintigraphy. All of these basins were identified by the study surgeon using the MGC device in the pre-operative setting prior to un-blinding. In every case the operative plan established based on pre-operative MGC imaging was confirmed by the FGC images. In two cases, additional information from the MGC images aided surgical decision-making. 5 of 22 lymph node basins were positive for metastasis. All of these basins were identified by pre-operative MGC imaging, and all individual positive nodes were identified by intra-operative MGC imaging. Conclusions: Pre-operative MGC imaging in sentinel lymph node biopsy can provide comparable information for operative planning, compared to standard FGC imaging.