“…Retrospective cohort studies comprised the majority of the included studies, with five (citations 44, 45, 47, 49, 53) being prospectively designed. Among the 15 studies included, four ( 39 , 41 , 42 , 46 ) were performed in the United States, five ( 40 , 44 , 47 , 50 , 52 ) in Italy, four ( 45 , 48 , 49 , 53 ) in Spain, one ( 51 ) in China, and one ( 43 ) in France. All patients in the 15 studies had solid tumors: three of the studies ( 41 , 48 , 51 ) involved patients with lung cancer, one study ( 46 ) included patients with gynecological tumors, and another study ( 45 ) included patients with melanoma; the remaining 10 studies were not specific as to cancer type.…”