“…Of the 33 included studies, only 12 looked at samples with heterogeneous primary cancers [ 6 , 8 , 20 , 26 , 28 , 29 , 31 - 34 , 37 , 38 ]. Of the 21 studies that looked at patients with only one primary cancer, seven looked at patients with lung cancer [ 12 - 14 , 23 , 25 , 30 , 36 ], four studies observed patients with only head and neck cancers [ 9 , 16 , 24 , 27 ], two looked at only prostate patients [ 7 , 11 ], another two focused on breast patients [ 18 , 21 ], those with only gynecologic cancers were examined in two studies [ 17 , 35 ], one study focused on gastric carcinoma patients[ 19 ], one study analyzed patients with hepatocellular carcinoma [ 15 ], another examined renal cell carcinoma patients [ 22 ] and a further study enrolled patients with pancreatic cancer [ 10 ].…”