Minimal Residual Disease in Head and Neck Cancer and Esophageal Cancer.

Malignant epithelial tumors of the upper digestive tract are a major cause of cancer-related death worldwide. The most common of these cancers are head and neck squamous cell carcinomas (HNSCC) and esophageal cancers (EC), which are both characterized by early dissemination and poor prognosis. Although patients with early detected cancers can be subjected to multimodal therapies with curative intention, they are endangered by lethal relapses that frequently occur. These relapses originate from minimal residual cancer (MRD) cells that can only be traced by highly sensitive molecular methods as rare disseminated tumor cells (DTC). The aim of this chapter is to comprehensively inform the reader about the detection, the mode of spread, the clinical relevance, and the biology of DTCs in HNSCC and EC. A better understanding of DTCs will be key to suppress progression of the upper digestive tract cancers more effectively.