Background: Metastastic teratoma (MT) is a unique germ cell tumor (GCT) subhistology characterized by resistance to platinum-based chemotherapy. Metastatic teratoma requires complete surgical excision, usually via retroperitoneal lymph node dissection (RPLND), following chemotherapy as a part of multidisciplinary GCT care. Molecular characterization of post-chemotherapy metastatic teratoma along with companion pre-chemotherapy testicular primary tumors could inform 1) the origin and differentiation site of metastatic teratomas, 2) mechanisms of platinum-resistance, 3) novel therapeutic options for patients with unresectable teratomas. Methods: We performed integrated molecular analysis for 16 primary germ cell tumors and 18 metastatic teratomas, 11 were matched tumor/metastasis pairs. All teratomas in our cohort were collected after induction platinum-based chemotherapy. In addition to SNV analysis, we conducted a chromosomal copy number gain and loss analysis for selected teratomas, matched primary tumors and primary teratomas from the TCGA. Results: Metastatic teratomas as well as their tumors of origin had low tumor mutation burden (0.65 and 0.47 accordingly). Amongst 583 SNVs detected in the study cohort, only two (KRAS p.Gly12Asp and KRAS p.Gly12Val) were previously described as oncogenic. Analysis of SNVs in proteins playing key roles in oncogenic signaling [1] showed that TP53 and Ras pathways were the most affected in metastatic teratomas. The majority of metastatic teratomas possess gain of 3p11.1 and loss of 10q26.3, 16p11.2, 19p13.2, 19q12 and 22q12.3 loci. Within 3p11.1 we did not identify any previously described oncodrivers. However, 5 chromosomal loci with lost heterozygosity contained 16 previously annotated tumor suppressor genes (15 protein coding and 1 microRNA, MIR199A1). Amongst those, GADD45GIP1 inhibition (growth arrest and DNA-damage-inducible, gamma interacting protein 1) is known for playing a role in cisplatin resistance through mechanism of cellular senescence [2]. Conclusions: Metastatic teratoma in our cohort is characterized by low tumor mutational burden, recurring copy number changes, and lack of recurring SNVs. Molecular insight of teratoma may inform disease biology and treatment. References: Sanchez-Vega, Francisco et al. “Oncogenic Signaling Pathways in The Cancer Genome Atlas.”Cell vol. 173,2 (2018): 321-337.e10. Nakayama, Kentaro et al. “Nucleus accumbens-1/GADD45GIP1 axis mediates cisplatin resistance through cellular senescence in ovarian cancer.”Oncology letters vol. 13,6 (2017): 4713-4719.