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Introduction to Carcinoid Tumors
Carcinoid tumors of the lung can be divided into two types:
Typical carcinoids which grow slowly and only rarely spread beyond the lungs. They are usually found along the major airways and, according to the American Cancer Society, are approximately nine times more common than atypical carcinoids.
Atypical carcinoids are faster growing tumors and are more likely to spread to other organs. They are also more likely to be located in the peripheral areas of the lung.
Although estimates vary, studies indicate that the incidence of carcinoid tumor by area of involvement is as follows:
- Small intestines - up to 30% of carcinoids
- Lungs - up to 25% of carcinoids
- Appendix - approximately 20%
- Rectum -12 to15%
- Colon - 10%
- Stomach - 3%
Other locations for carcinoid tumors (e.g., testis, ovary, larynx) are infrequent or rare and account for only about 3 to 5% of all carcinoid tumors. It is estimated that in up to 15% of patients with carcinoid tumors, distant metastases have developed by the time they are diagnosed with a carcinoid tumor.
The potential for malignant growth of carcinoid tumors appears to be related to several factors including:
- The site at which the tumor originates
- The depth of tumor invasion into adjacent tissue
- The size of the tumor
It is estimated that approximately 10% of patients with carcinoid tumors develop carcinoid syndrome that manifests itself with symptoms related to the various substances produced by the tumors. A more detailed description of carcinoid syndrome follows later in this section.
