OBJECTIVE: This study aimed to investigate the progression type of metastatic breast cancer (MBC) in patients undergoing eribulin chemotherapy.
METHODS: We retrospectively investigated the cases of 66 consecutive patients with MBC who underwent eribulin chemotherapy.
RESULTS: A total of 15 patients (22.7%) received eribulin as a 3rd-line or later treatment, and 17 (25.8%) received eribulin as a 1st-line treatment. The overall response was complete response in 0 (0%), partial response in 15 (22.7%), stable disease in 27 (40.9%), and progressive disease in 24 (36.4%) patients. By the time of data cut-off, time to treatment failure (TTF) events had been observed in 60 patients (90.9%), among whom, 15 (25%) had disease progression due to NM, and 45 (75%) had disease progression due to PL. In the regimen before eribulin administration, among 49 patients, 24 (49.0%) had disease progression due to NM. Luminal-type patients and those with triple-negative breast cancer exhibited a similar tendency, i.e., the rate of NM was lower in the patients treated with eribulin. The rate of NM was lower in the patients treated with eribulin in the 1st-line setting than that in patients treated with eribulin as a later treatment.
CONCLUSIONS: Eribulin has a potential antitumor mechanism to prevent new metastasis. Eribulin may be effective against both the epithelial-mesenchymal transition (EMT) process and new metastasis.

BACKGROUND: There is growing evidence that patients with metastatic breast cancer whose disease progresses from a new metastasis (NM) have a worse prognosis than that of patients whose disease progresses from a pre-existing metastasis. The aim of this pilot study is to identify a blood biomarker predicting NM in breast cancer.
METHODS: The expression of epithelial (cytokeratin 18/19) or mesenchymal (plastin-3, vimentin, and N-cadherin) markers in the peripheral blood (PB) of recurrent breast cancer patients undergoing chemotherapy with eribulin or S-1 was measured over the course of treatment by RT-qPCR. The clinical significance of preoperative N-cadherin expression in the PB or tumor tissues of breast cancer patients undergoing curative surgery was assessed by RT-qPCR or using public datasets. Finally, N-cadherin expression in specific PB cell types was assessed by RT-qPCR.
RESULTS: The expression levels of the mesenchymal markers N-cadherin and vimentin were high in the NM cases, whereas that of the epithelial marker cytokeratin 18 was high in the pre-existing metastasis cases. High preoperative N-cadherin expression in PB or tumor tissues was significantly associated with poor recurrence-free survival. N-cadherin was expressed mainly in polymorphonuclear leukocytes in PB.
CONCLUSIONS: N-cadherin mRNA levels in blood may serve as a novel prognostic biomarker predicting NM, including recurrence, in breast cancer patients.