Carcinoid tumors are malignant tumors (usually of the neuroendocrine system) that only rarely metastasize. Because they do not readily spread, many patients with them have good prognoses, either with surgical treatment or even in absence of treatment, despite the fact that chemotherapy is not usually effective on these tumors.

The intriguing question is why. Neuroendocrine tumors as a class tend to follow the pattern of poor response to chemotherapy and relative indolence, despite what appears to be going on histologically. If we could figure out the conditions that favor such a pattern, we could perhaps design more effective treatments for other types of malignancies as well.