We investigated the ADA1 and ADA2 activities in serum from cancer patients, including CESC, CHOL, colon adenocarcinoma (COAD), ESCA, GBM, LIHC, LUAD, OV, KIRC, KIRP, PAAD, PRAD, rectal adenocarcinoma (READ), SARC, STAD, THCA, and UCEC. Here, ADA2 is linked to cancer.