Sinonasal Teratocarcinosarcoma (SNTCS) is a rare and histologically heterogeneous tumor of uncertain origin and unknown molecular pathogenesis. Its location and aggressiveness, with frequent recurrences, high rate for metastasis and short mean survival, make SNTCS a tumor highly difficult to treat. Thus, the identification of underlying genetic changes could potentially provide successful adjuvant or alternative precision medicine treatment options for patients with this tumor. We report here a 55-year-old male with a naso-ethmoidal SNTCS that invaded right maxillary sinus, orbital cavity and cranial anterior fossa and that was treated with surgery followed by radiotherapy and chemotherapy in which we evaluated the mutational profile by multigene panel sequencing. Tumor and adjacent normal mucosa were screened for hotspots and targeted regions of 22 cancer related genes by multigene panel sequencing. The analysis revealed a somatic pathogenic mutations in the PIK3CA gene (p.His1047Leu) and a germline alteration in the DDR2 gene (p.Pro476Leu) whose oncogenic function is considered unknown. This study suggests the involvement of PIK3CA gene mutation in SNTCS tumorigenesis highlighting a potential target for individualized molecular therapy for patients with this tumor.