Establishment of a Microfluidic Based Liquid Biopsy Platform for Recurrent/Metastatic Head and Neck Cancers Prognostication Using NK Cell IFN-γ Expression and CTM Correlation With DS-SACA Chip

The goal of this observational study is to learn about the prognostic value of circulation tumor emboli (CTM) in recurrent/metastatic head and neck cancer patients and also the changes of tumor microenvironment by different treatment modalities and drugs. The main questions it aims to answer are: 1. Investigators plan to correlate circulating tumor cells (CTC), circulating tumor emboli (CTM), and the composition of NK cells in CTM with clinical outcomes and establish their association with patient prognosis. 2. Investigators plan to understand the composition of NK cells and the immune cell components within CTM, and correlate these findings with treatment efficacy. Patients with recurrent/metastatic head and neck cancer will be included after informed consent and investigators will collect blood samples for analysis from them under the treatment provided by their primary care physicians.