For functional studies in esophageal cancer, studies can be performed in cancer cell lines derived from tissues obtained freshly from surgery. Cancer cell lines need proper medium to grow. Cancer cell lines often grow without attaching to a surface, and they can proliferate to a very much higher density in a culture dish. The resulting transformed cancer cell lines, in reciprocal fashion, can often cause tumors if injected into a susceptible animal to generate an animal model. Cancer cells can be harvested from the animal and form a more stable cancer cell line. In esophageal cancers, some of the commonly used cell lines are actually secondary cell lines. Cancer cell lines can allow functional studies to be performed. They can be stored in liquid nitrogen for an indefinite period and retain their viability when thawed.

In esophageal cancers, there are published cancer cell lines available for both adenocarcinoma and squamous carcinoma [76–79]. When compared to esophageal squamous cell carcinoma, esophageal adenocarcinoma is more uniform in characteristics as the risk factors and pathogenesis are more established. Model research on esophageal adenocarcinoma relies almost entirely on a relatively small set of established cancer cell lines. The high genomic similarities between the esophageal cell lines and their original cancers provide rationale for their use. Nonetheless, cancer cell lines nearly always differ in important ways from the original cancer from which they were derived.

Animal models are important to study the effects of cancer in vivo and also for the production of cancer cell lines. In more clinical relevant applications, an animal model is a must for developing therapeutic strategies. Cancer development is a complex process with the accumulation of genetic alterations and their downstream effects as well as interactions with the microenvironment in different tissues. The cancer microenvironment and its interactions with the cancer are important in determining the growth dynamics of different cancers.

Injection of cancer or cancerous cells in the subcutaneous tissue of the skin of immunodeficient mice is a common practice to produce a cancer model in animals (Fig. 2.4). In esophageal cancers, this approach cannot recapitulate the microenvironment of the esophagus or the response to the targeting carcinogens. The current approach is to make an orthotopic (occurring at normal place) model for both esophageal squamous cell carcinoma and esophageal adenocarcinoma [80, 81]. The orthotopic model provides the most optimum environment for cancer growth and drug testing. In the anatomical setting of esophageal cancer, the site is very difficult to approach surgically. Different approaches have been applied but many of these have some shortcomings. The establishment of these orthotopic models needs to involve radiological guidance (magnetic resonance imaging and fluorescence imaging) so the cancer and the metastases can be visualized in real time [82]. In addition, pathological examination is important to clarify the histological typing, microscopic location, and the microenvironment of the cancer in the animal [83].