GPC3 and Merkel cell skin cancer: In order to validate the GPC3 IHC assay using GC33 antibody for use as a lab-developed test for clinical trials, Tissue microarray (TMA) slides or whole mount slides containing tumor samples from HCC, liposarcoma, lung cancer, and MCC patients were stained by GPC3 IHC assays using either GC33 or previously validated 1G12 antibody clones.