116 Mosaic RASopathies associated with rhabdomyosarcoma OM Davies 1 , A Bruckner 2 , T McCalmont 3 , V Oza 4 , M Williams 3 , L Wine Lee 5 and DH Siegel 1 1 Medical College of Wisconsin, Milwaukee, Wisconsin, United States, 2 University of Colorado School of Medicine, Aurora, Colorado, United States, 3 University of California San Francisco, San Francisco, California, United States, 4 New York University School of Medicine, New York, New York, United States and 5 Medical University of South Carolina, Charleston, South Carolina, United States Rationale: RAS genes are well-established oncogenes known to contribute to the develop- ment of cancer. Epidermal, sebaceous, and melanocytic nevi may be triggered by somatic mutations in HRAS, KRAS, and NRAS. The majority of these nevi are not associated with internal malignancies, however, a small subset have been associated with rhabdomyosar- coma (RMS). This calls into question the clinical utility of the anatomic location of the nevi for cancer risk stratification and management. Methods: A retrospective review showed 12 previously reported cases of RAS-driven nevi in conjunction with RMS. 3 additional unre- ported cases were collected from collaborators through the Pediatric Dermatology Research Alliance (PeDRA). Results: 15 patients with 16 primary RMS were included for analysis. 12/15 were previously reported. 1-12 All had RAS-driven birthmarks: 5 patients with epidermal nevi, 4 with congenital melanocytic nevi, 4 with phacomatosis pigmentokeratotica, and 2 with speckled lentiginous nevi/agminated Spitz. Of the 16 RMS: 8 were genitourinary, 3 were pelvic/retroperitoneal, 4 were dermal, and 1 was abdominal. 5/15 tumor-birthmark pairs had genotyping results: 3 had HRAS mutations and 2 had KRAS mutations. Body surface area did not seem to be a contributing risk factor. However, all 15 cases had involvement of the nevus on the trunk. Relevance: Truncal location of mosaic RASopathies may be a risk factor for RMS. Further prospective studies are needed to solidify appropriate monitoring guidelines for patients at risk. 117 Small non-coding RNA SNORA12 effects MAPK1 signaling Z Siprashvili 1 , RM Shenoy 1 , L Elcavage 1 and PA Khavari 1,2 1 Dermatology, Stanford University, Stanford, California, United States and 2 VA Palo Alto Healthcare System, Palo Alto, California, United States Small non-coding RNAs play fundamental roles in biology. Among them are snoRNAs, which are best studied for their role in modifying RNA nucleosides. Of the two major snoRNA classes, H/ACA box snoRNAs are known to enable RNA pseudouridylation while C/D box snoRNAs facilitate RNA methylation.137/412 annotated snoRNAs do not have defined RNA targets, and are designated as orphan snoRNAs. Recent data suggest that snoRNAs may have broader impacts relevant to human disease, including in genetic disorders, metabolic stress, and neoplasia. To identify new roles for snoRNAs in disease, we hybridized all non-clustered orphan snoRNAs consist of 26 C/D and 20 H/ACA box snoRNAs to 9200 recombinant human proteins. Unexpectedly, the H/ACA box snoRNA SNORA12 directly bound an essential ki- nase in the MAPK protein kinase cascade, ERK2 (MAPK1). A CRISPR/Cas9 dual-cut gRNA lentiviral vector was used to produce SNORA12snoRNA knockout clones from human cancer cell lines. SNORA12 deletion reduced ERK2 activation and in vivo tumorigeneses. These effects were due to the SNORA12 snoRNA itself, as opposed to an artifact of genome editing at the SNORA12locus, as confirmed by rescue experiments that restored SNORA12 expres- sion. To define how SNORA12 modulates ERK2 function, we performed mass spectrometry (LC-MS/MS) to detect ERK2 proximal proteins in the presence and absence of SNORA12. In parallel, we also analyzed the status of 104 phosphorylation sites on 62proteins relevant to MAPK signaling in wild-type and SNORA12knockout cells. Taken together, the resulting data demonstrated that SNORA12 controls ERK2 kinase activity by modulating ERK2 protein- protein interactions in highly specific ways. These findings identify SNORA12 as a new essential regulator of MAPK signaling in cancer and further extend the biological roles for small non-coding RNAs to the control of cellular signal transduction. 118 Inhibition of p38 re-expresses e-cadherin and prevents vascular invasion in melanoma J Wenzina 1 , S Holzner 1 , A Forsthuber 1 , E Puujalka 1 and P Petzelbauer 1,2 1 Skin and Endothelium Research Department, Medical University of Vienna, Vienna, Austria and 2 Division of General Dermatology and Dermatooncology, Medical University of Vienna, Vienna, Austria Melanoma is arising from melanocytes residing in the basal layers of the epidermis or from nevi. In the initial phase, melanoma cells spread horizontally within the epidermis. These cells can vertically invade into the dermis causing invasive disease associated with a signif- icant risk for metastasis. Invasive cells differ from primary tumor cells by their phenotype and growth behavior. This heterogeneity was described by “proliferative” and “invasive” gene signatures. Melanoma can switch back and forth between these phenotypes, pointing to environmental triggers. By correlating mRNA expression levels of a set of 22 patient-derived melanoma cell lines, E-cadherin/CDH1 expression emerged as the single best marker for a proliferative phenotype. To define the underlying signaling pathway in vitro and in vivo, we used CDH1 as a surrogate marker. We found CDH1 positivity correlating with active JNK and CDH1 negativity with active p38/MK2 signaling. Blocking p38/MK2 re-induced CDH1, blocking JNK eliminated CDH1 expression, postulating that an invasive phenotype correlates with p38/MK2 signaling. This was confirmed by using assays probing for vascular invasion. Melanoma cells with an active p38/MK2 signaling induced vascular barrier disruption and endothelial retraction in vitro and were able to seed to lungs after tail vein injection, which was reduced by p38/MK2 inhibition. JNK signaling is responsible for the proliferative phenotype whereas p38 activation leads to an invasive phenotype and hence to high levels of VEGF-C and therefore contributes to lymphangiogenesis. Blocking the p38/MK2 pathway may serve as an adjuvant treatment option to prevent vascular dissemination of melanoma. 119 Genetic alterations in cutaneous squamous cell carcinoma arising in immunocompromised patients: a review of the current literature M Lobl 1,3 , S Higgins 1 , A Sutton 1 , R Trowbridge 1 , J Mott 2 and A Wysong 1 1 Dermatology, University of Nebraska Medical Center, Omaha, Nebraska, United States, 2 Biochemistry, University of Nebraska Medical Center, Omaha, Nebraska, United States and 3 Eppley Cancer Institute, University of Nebraska Medical Center, Omaha, Nebraska, United States Cutaneous squamous cell carcinoma (SCC) is the most common malignancy post-transplant in organ transplant recipients (OTRs). OTRs are 65-250 times more likely to develop SCCs than the general population. In addition, SCC in OTRs behaves differently than SCC in immunocompetent patients (ICPs). There have some reports in the literature in which various genetic differences between SCCs in these two populations were compared. However, there is no current study that synthesizes these reports and provides a springboard for which to guide future studies. This research aims to discuss currently reported differences in the literature regarding differences in gene expression in SCCs between these two populations in order to aid clinician management and to facilitate further research. A literature search was conducted in December 2018 in both MEDLINE via PubMed and Embase using key words that included squamous cell carcinoma, skin, cutaneous, transplant, immunosuppression, immunocompromised, genetics, and genes. A total of 29 papers were returned from this search, and after screening 15 remained. SCCs in OTRs have distinct genetic alterations, which especially affect the tumor microenvironment. SCCs arising in OTRs have a marked decrease in Th1 mediators in the tumor microenvironment, which may help to explain the aggressive behavior. SCCs in OTRs have fewer overall genetic changes than expected in ICPs, and epigenetic changes marked by changes in methylation patterns. The differences in gene expression in SCCs arising in OTRs compared to SCCs arising in ICPs likely cause tumors to behave differently between these two populations. In addition, these changes in gene expression determine which tumors will respond to specific therapies, necessitating the development of unique therapies for the OTR population. 120 The novel AKT inhibitor afuresertib inhibits Merkel cell carcinoma through targeting TSC-mTOR and GSK-3 pathways J Wu, A Limmer, H Doan, R Simonette, P Rady and S Tyring UT Health Science Center, Houston, Texas, United States The Merkel cell polyomavirus (MCPyV) is the causative agent in 80% of Merkel cell carci- nomas (MCCs), and recent studies have shown that MCPyV’s oncogenic mechanism is dependent upon viral activation of key molecular targets including mTOR. Consequently, inhibition of the mTOR pathway has shown significant promise for future treatment of MCC. In the current study, we identify AKTas a key modulator of mTOR in MCC cells. We analyzed the effect and mechanism of the novel AKT inhibitor, afuresertib, in human MCC cells derived from MCPyV-positive MCCs (MKL-1). Our data show that treatment of MKL-1 cells with afuresertib resulted in marked dephosphorylation and subsequent deactivation of mTOR via dephosphorylation of TSC and PRAS40. Accordingly, afuresertib reduced the activation of two mTOR downstream targets, 4EBP1 and S6K. In addition to inhibition of the mTOR pathway, afuresertib treatment also led to the dephosphorylation and deactivation of GSK3, a key molecule that regulates cell metabolism, proliferation and survival. Next, we examined the effect of afuresertib on MCC cell proliferation. Our data showed that treatment of the MKL-1 cells with afuresertib resulted in marked inhibition of cell proliferation, with 45% reduction at 5mM and 80% reduction at 10mM. Our data demonstrate that the AKT inhibitor afuresertib blocks both the TSC-mTOR and the GSK3 signaling pathways and these effects lead to robust inhibition of MCC cell growth. As mTOR inhibitors are currently being investigated in clinical trials for MCC patients, our findings may have important implications for future treatment of MCC, especially considering that afuresertib simultaneously inhibits both the TSC-mTOR and GSK3 pathways and thus may provide more effective anti-tumor action than mTOR inhibitor alone. To our knowledge, this is the first report describing the effect of afuresertib in MCC. Our findings warrant further investigation to delineate the mechanism of AKT regulation in MCC cells and to evaluate the efficacy of targeting AKT for the treatment and management of MCC. 121 Prognostic value of INPP5A expression in recurrent and metastatic cutaneous squamous cell carcinoma CJ Maly 1 , H Cumsky 1 , C Costello 1 , J Montoya 1 , J Schmidt 1 , D DiCaudo 1 , S Nelson 1 , D Butterfield 1 , N Zhang 1 , M Smith 2 , S Ochoa 1 , C Baum 3 , T Nagel 4 , M Pittelkow 1 , A Sekulic 1 and A Mangold 1 1 Dermatology, Mayo Clinic, Scottsdale, Arizona, United States, 2 Pathology, Mayo Clinic, Scottsdale, Arizona, United States, 3 Dermatology, Mayo Clinic, Rochester, Minnesota, United States and 4 Otolaryngology, Mayo Clinic, Scottsdale, Arizona, United States Introduction: Inositol polyphosphate-5-phosphatase (INPP5A), a membrane-associated type I inositol phosphatase, has been shown to play a role in the progression of a pre-malignant lesion to cutaneous squamous cell carcinoma (cSCC) and the progression of localized disease to metastatic disease in oropharyngeal SCC and cSCC. INPP5A loss in primary tumors is asso- ciated with aggressive disease and a poor overall survival. The prognostic value of INPP5A in recurrent and metastatic disease (RMD) cSCC is unknown. We hypothesize that loss of INPP5A expression level in RMD cSCC will correlate with aggressive disease and predict a poor outcome. Methods: Immunohistochemical staining was used to examine INPP5A protein expression in cSCC in both primary tumors and RMD. The cases were identified through our retrospective cSCC database. Overall survival (OS) was compared based upon INPP5A expression (high stain expression HSE, low stain expression LSE) at the primary tumor level, change in INPP5A status from primary tumor to RMD, and a composite risk score (CRS) (CRS¼primary + RMD with HSE¼0 &LSE¼1; range 0-2) using log-rank test and Cox regression model. Results: 58 tumors and 70 RMD events were evaluated from 52 patients. 10 primary tumors had multiple events. LSE of INPP5A in RMD was associated with poor OS (median survival time 31.0 months for LSE, 62.0 months for HSE, p ¼ 0.027). CRS of 0 was predictive of improved OS at 2 years compared to CRS of 1 (HR 0.42, 95% CI: 0.21-0.84, p ¼ 0.011). Discussion: INPP5A appears to be a predictor of poor OS in both primary and RMD of cSCC. An additional study in larger cohorts is justified in order to determine if INPP5A expression may serve as a biomarker to stratifying OS in individuals with RMD. Carcinogenesis and Cancer Genetics | ABSTRACTS www.jidonline.org S21