GPC1 and pachyonychia congenita: Previous studies have reported that GPC-1 is specificallyenriched on cancer-cell-derived exosomes.12,13 It has been found that PC patients express higher levels of GPC-1on their exosomes than healthy controls with high specificity andsensitivity for PC.14 Other exosome-basedproteins such as epidermal growth factor receptor (EGFR)4 and epithelial cellular adhesion molecule (EpCAM)15 also show high accuracy and selectivity forPC detection.