To address the challenges of isolating and analyzing rare cells, this study aims to validate the instrumentation, the test protocols, and the analysis of patient's outcome to show the instrument's capability to reproducibly and accurately detect CTCs in cancer patients. In order to facilitate the validation process, investigators will only focus on metastatic patients for whom CTCs supposedly present at higher abundance. Investigators propose to enroll cohorts of metastatic breast cancer patients. Blood samples will be collected from these patients before they start any new line of therapy as determined by their doctors. The specific aims are to isolate, enumerate and analyze the number and/or molecular information of circulating tumor cells in patient blood using microfluidic chip-based sorting, imaging, and molecular profiling techniques. Investigators will use this study to optimize diagnostic instrumentation, test blood processing protocols and CTC analysis algorithm. During this study investigators will collect patients' clinical information related to cancer, as well as the patients' survival status to validate the system's prognosis ability.

Inclusion Criteria:

1. Provision of signed written informed consent before enrollment into the study, ability to communicate with the investigators, and to understand and comply with the requirements of the study.
2. Progressive and measurable metastatic breast cancer.
3. Commencement of new anti-cancer chemotherapy or palliative care.
4. ECOG performance status equal or less than grade 2.

Exclusion Criteria:

1. Subject has received any investigational agent, not explicitly approved by MiCareo, within last one year.
2. Subject being identified with any blood borne infectious disease.
3. Subject has received anticancer chemotherapy within last one month. (not including hormone therapy, or target therapy)
4. Pregnancy.

metastatic breast cancer (mBC) patients