SMN1 and head and neck squamous cell carcinoma: To test the in vivo ability of SMA-positive fibroblasts, generated either through TGF-β1 treatment or senescence induction, to produce and remodel collagenous ECM, we used a HNSCC cancer xenograft model (5PT) [34], co-injecting tumor cells with TGF-β1-treated or irradiated fibroblasts.