Aim: To investigate whether plasma C-MYC level could be an indicator in clinical 
progression of breast cancer. Materials & methods: Plasma level of C-MYC 
expression was detected by quantitative real time PCR and the level of c-myc 
protein in breast cancer tissues was detected by immunohistochemistry. The 
expression level of C-MYC mRNA in supernatant of cancer cells culture was 
measured compared with the nonbreast cancer cells. Results: Plasma C-MYC level 
was significantly higher in patients with breast cancer than that in the 
controls, which associated with clinical stages, lymph node status, etc. 
Receiver operating characteristic curve analysis showed the sensitivity and 
specificity of plasma C-MYC level for diagnosis of breast cancer were 63.6 and 
81.8%, respectively. The expression of c-myc protein in breast cancer tissues 
was associated with plasma C-MYC level, even C-MYC level in supernatant of 
cancer cells was elevated. Conclusion: Plasma C-MYC level might be a potential 
indicator in progression of breast cancer.