RET and cancer: Moreover, limited response and progression-free survival (PFS) benefit has been shown with immunotherapy, possibly due to low levels of Programmed Death Ligand 1 (PDL1) expression and low mutation burden.35 The first potential for targeting RET alterations came historically from studies that were done on MKIs.2 Cabozantinib and vandetanib have emerged, among other MKIs, in that regard as key players with evidence of their activity in RET-altered cancers.