Despite advances in medicine, we are not yet at a stage where we are safe from cancer, although many types are now treatable. Carcinoid tumors are a rare form of cancer. Their etiology remains unclear; however, there are several genetic syndromes that can be associated with this condition (i.e. Multiple Endocrine Neoplasia). Carcinoid tumors will usually have slow growth, and will rarely cause specific signs or symptoms.
A small percentage of carcinoid tumors may be “functioning” and secrete chemicals (hormones) that can cause a condition known as carcinoid syndrome, while others may be “non-functioning” and not produce early signs or symptoms. Because hormone-producing tissues constitute the origin of carcinoid tumors, many of the side effects of this condition can be associated with incorrect levels of diverse hormones in the body.
Finally, the diagnosis of a carcinoid tumor is difficult, and it may be an incidental finding on surgical procedures (i.e. appendectomy), histopathology, or imaging.
1. Carcinoid Tumor
Carcinoid tumors are a subtype of neuroendocrine tumors, cancers that start in cells known as neuroendocrine cells. These are specialized cells that can receive information from nerve cells (neuronal input) and, as a result, release hormones into the bloodstream. Importantly, hormones are chemical ways of sending specific messages through the blood to different organs or tissues of the body, in order to exert particular functions. Neuroendocrine cells can be found throughout the body; given that they have a role in controlling many important bodily functions. Thus, carcinoid tumors can be located in the respiratory tract (lungs, trachea, bronchus), liver, gastrointestinal tract (rectum, appendix, ileum), ovaries, kidneys, prostate, and testes. Finally, roughly ninety percent of these tumors arise from the appendix or terminal part of the ileum (small intestine).
Most carcinoid tumors (mostly “nonfunctioning” types) will often go unnoticed until they reach an advanced stage because they rarely cause early signs or symptoms. The clinical manifestations in these types of tumors will depend on their size and location. Other carcinoid tumors, especially “functioning” tumors, can cause several symptoms of carcinoid syndrome.
Treatment for carcinoid tumors will generally involve medication (i.e. chemotherapy), but surgery may also be performed in specific cases. In general, the outcome for patients with distant spread of the tumor (metastasis) is poor; however, localized and resected carcinoid tumors have a great prognosis.