AbstractMac‐2 binding protein (Mac‐2BP) is a secreted tumor antigen that is elevated in many cancers and implicated in tumor metastasis, as well as cell adhesion and immune functions. We focused on the human telomerase reverse transcriptase (hTERT) induced Mac‐2BP expression and the relationship between Mac‐2BP expression and the progression of gastric cancer. A cDNA expression array analysis was performed on the telomerase‐negative cell line, SW13, which was engineered to overexpress hTERT when compared with the parental SW13 cell. hTERT‐induced Mac‐2BP expression was confirmed via RT‐PCR and Northern blotting. ELISA and flow cytometric analyses revealed that Mac‐2BP protein was increased by 2‐ to 4‐fold in hTERT‐overexpressing cells compared with the mock control. Mac‐2BP expression was significantly reduced when the overexpressed hTERT was neutralized by the introduction of hTERT‐specific siRNA. These results suggest that Mac‐2BP expression is modulated by hTERT. Mac‐2BP levels in both gastric cancer cells and tumor tissues were determined via Northern blot analysis and immunohistochemistry. Mac‐2BP protein was highly expressed in most gastric cancer cell lines, and gastric tumor tissues were stained more densely than normal tissues. The intracellular and secreted Mac‐2BP levels were also evaluated via ELISA, indicating that Mac‐2BP was expressed and secreted more abundantly in gastric cancer patients than in healthy donors. The elevated serum Mac‐2BP level in gastric tumor patients was also significantly associated with distant metastasis (p = 0.05) and higher tumor stage (p = 0.04). Our findings suggest that Mac‐2BP is induced by hTERT, and that it may prove to be a useful prognostic marker for the detection of malignant progression of metastatic stomach cancers. © 2006 Wiley‐Liss, Inc.