PDGFD and head and neck squamous cell carcinoma: A recent study by Álvarez-Teijeiro et al. identified several proteins differentially secreted in CAF-conditioned medium compared to normal fibroblasts, including EGF containing fibulin-like extracellular matrix protein 1 (EFEMP1), platelet derived growth factor D (PDGFD) and insulin-like growth factor binding proteins 5/7 (IBP5/IBP7) that may be responsible for sustaining the cancer stem cell phenotype in HNSCC [276].