The development of telangiectasia in four patients in this study (three with a primary diagnosis of HCC) suggests vascular targeting and in vivo inhibition of the ALK‐1 pathway by PF‐03446962, consistent with the genetically determined loss of ALK‐1 functions reported in patients with type 2 HHT 7, 8, 9. This evidence concerns the gene ACVRL1 and telangiectasis.