The PDI repertoire detected by LC–MS/MS-based label-free semi-quantitative proteomic analysis in 22 cancer cell line lysates to some extent was specific to the cell type (Table 1) and included the following PDI isoforms: PDIA1 (P4HB), PDIA3 (ERp57), PDIA4 (ERp72), PDIA6 (ERp5), PDIA9 (ERp29), PDIA10 (ERp44), PDIA15 (TXNDC5), PDIA16 (TXNDC12), PDIA 17 (PDIA17) and PDIA18 (ARG3). The gene discussed is PDIA4; the disease is cancer.