Intratumoral injection of immune-modulatory compounds is a potentially feasible delivery approach, with administration of recombinant IL-12 (for head and neck squamous cell carcinoma (H&NSCC) [49] and viral vectors encoding cytokine genes IFN-γ [50], GM-CSF [51] (both for melanoma) and IL-12 [52] (colorectal and pancreatic cancers) already being evaluated in clinical trials. This evidence concerns the gene CSF2 and head and neck squamous cell carcinoma.