Distinction of head & neck squamous cell carcinoma (HNSCC) and lung squamous carcinoma (lung SCC) cancers by GEP-HN-LS. H&E stained sections (A and B) of a metastatic lung SCC carcinoma (A) and a metastatic HNSCC carcinoma (B) from the validation specimens show well-differentiated squamous cell morphologic appearance. GEP-HN-LS clearly distinguished between these metastatic tumors. GEP-HN-LS test results were lung SCC with a Similarity Score of 82.6 for the metastatic lung SCC cancer (A) and HNSCC with a Similarity Score of 99.1 for the metastatic HNSCC cancer (Photographs A and B taken at 10X objective magnification). Both poorly differentiated lung SCC (C, E) and HNSCC (D, F) cancers from the validation specimens show positive immunohistochemical staining for p63 (C, D) and CK5/6 (E, F), common biomarkers for squamous cell carcinomas. GEP-HN-LS test results for these cancers were lung SCC with a Similarity Score of 100 for the poorly differentiated lung SCC cancer (C, E) and HNSCC with a Similarity Score of 93.8 for the poorly differentiated HNSCC cancer (D, F) (Photographs C, D, E and F taken at 20× objective magnification; Bars equal 50 μm).