Molecular detection of CK-19 mRNA-positive cells by RT-PCR in the peripheral blood of patients with stages I and II breast cancer before initiation of adjuvant therapy has independent prognostic value as a marker of poor clinical outcome.

Detection of peripheral-blood CK-19 mRNA-positive cells is an independent predictive and prognostic factor for reduced disease-free interval and overall survival, respectively, in node-negative breast cancer patients.

Detection of CK-19 mRNA-positive CTCs before adjuvant chemotherapy predicts poor clinical outcome mainly in patients with ER-negative, triple-negative, and HER2-positive early-stage breast cancer.