The aim of this study was to evaluate tumor markers of molecular abnormalities that display tissue specificity, as to detect circulating tumor cells (CTCs) in breast cancer patients. Quantitative real-time RT-PCR was used to determine h-MAM, BCSG1, CK19, and c-erbB2 mRNA levels in peripheral blood (PB) of breast cancer patients. Results were compared with other epithelial cancers (lung or esophagus cancer), benign breast disease, and healthy individuals. We found that h-MAM mRNA was only detectable in the PB of patients with breast cancer (49 of 65, 75.4%), but not in patients with other epithelial cancers, benign breast disease, or healthy individuals. No significant differences in the expression level and positive detection rate of BCSG1, CK19, and c-erbB2 mRNA were observed between breast cancer and other epithelial cancers. Furthermore, the expression level and positive detection rate of h-MAM mRNA in PB were significantly correlated to the breast cancer pathologic stage (p=0.012 and p=0.015, respectively). Chemotherapy, radiotherapy, or total tumor resection (after 7 days of treatment) resulted in a significant decrease in the expression level of h-MAM mRNA in PB compared to the levels prior to the treatment (p<0.001). Importantly, an increase in h-MAM mRNA expression was detected in patients immediately after surgery, as well as 3 days post-surgery. These results indicate that the quantitative analysis of h-MAM mRNA is a useful tool for detecting CTCs in breast cancer patients, and can have a potential diagnostic utility in early micrometastasis, clinical evaluation of cancer treatment efficacy, and post-treatment monitoring of breast cancer patients.