participants are no longer being examined or treated

We hypothesized that the number of circulating tumor cells (CTCs) and molecular markers on CTCs could be a prognostic factor or predictive factor to patients with head neck cancer.

1. Histologically or cytopathologically proven head and neck squamous cell carcinoma (HNSCC)

2. Disease status: locally advanced or recurrent/metastasized at initial presentation

3. Age >=20 years old

4. Could understand and signed the informed consents of this study

5. Enrolled patients were classified into three distinct subgroups:

   1. Patients underwent curative surgery followed by adjuvant chemoradiotherapy (CRT) because of some pathologic features such as positive margin, pathologic N2, and extracapsular spread (ECS) of involved lymph nodes indicating early relapse according to recommendation from National Comprehensive Cancer Network(NCCN) guidelines;
   2. Patients with advanced disease directly underwent definitive concurrent chemoradiotherapy(CCRT);
   3. Patients were to have palliative chemotherapy for existence of distant metastasis or poor general condition for definitive CCRT.

6. Blood samples were collected within 7 days before the first dose of chemotherapy.

Inclusion Criteria:

• histologically or cytopathologically proven head and neck squamous cell carcinoma Age ≥ 20 years. Measurable or evaluable disease according to Response Evaluation Criteria In Solid Tumors(RECIST) criteria.

Ability to sign informed consent.

Exclusion Criteria:

• Prior cancers within 5 years, except for non-melanoma skin cancers, and in situ cervical cancers.

Inability to comply with study and/or follow-up procedures.

Locally advanced or recurrent/metastatic head and neck cancer