GREM1 and neoplasm: Representative immunostaining images from OPSCC tumor samples demonstrates the presence of gremlin-1 positive cells (Fig. 1a–c) in the tumor microenvironment from patient OPSCC tumor samples and labeled cells distinct from the hematopoietic lineage markers CD14 (Fig. 1g–i) and CD45 (Additional file 1: Figure S1A–C) an important distinction for determining cells of mesenchymal lineage.