Among the transmembrane genes differentially expressed between the tumor and the surrounding nontumorous areas, we focused on tumor-associated calcium signal transducer 2 (TACSTD2) [24], also known as trophoblast antigen 2 (Trop2), because it was the second most downregulated gene within the tumor (Fig 1A and S1 Table) and showed a very strong correlation with HCV RNA levels (r = 0.71, P<0.00001) (S5B Fig). Here, TACSTD2 is linked to neoplasm.