Recent observations support the notion that telomerase expression is essential for the formation of human tumor cells [W-C. Hahn et al., Nature (Lond.), 400: 464-468, 1999]. The expression pattern of hTERT, the human telomerase catalytic subunit gene, is a rate-limiting determinant of the enzymatic activity of human telomerase. We have developed a real-time quantitative RT-PCR assay based on Taq-Man fluorescence methodology to quantify the full range of hTERT mRNA copy numbers. We validated the method on a series of 134 unilateral invasive primary breast cancer patients with known long-term outcome. Three-quarters of the breast tumors (75.4%; 101 of 134) were hTERT positive, i.e., contained detectable and quantifiable hTERT mRNA. hTERT-positive patients had significantly shorter relapse-free survival (P = 0.017) after surgery compared with hTERT-negative patients. The prognostic significance of hTERT status persisted in Cox multivariate regression analysis. When we subdivided hTERT-positive patients (n = 101) into three equal groups (tumors showing small, intermediate, or high increase in hTERT mRNA content), we observed statistical (or a trend toward) links between high hTERT mRNA levels and Scarff-Bloom-Richardson histopathological grade III (P = 0.066), and negative estrogen (P = 0.002) and progesterone (P = 0.048) receptor status, and therefore with higher aggressiveness of breast tumors. High hTERT mRNA levels were also linked to MYC gene overexpression (P = 0.007). These findings show that the quantitative evaluation of hTERT mRNA can have important prognostic significance in human breast cancer. In addition, our simple, rapid, and semiautomated assay method is suitable for routine hTERT mRNA detection and quantification and will be a powerful tool in large, randomized, prospective, cooperative group trials and in the hTERT-based therapy project.