Primary malignant neoplasms of the small bowel

In 1746, Hamburger described a small bowel carcinoma. The incidence ranges from 0.2 to 5% of all gastrointestinal cancers. Variability is dependent on whether one considers lymphomas, ileocecal valve, and periampullary lesions in the study. Especially with lymphomas, it is difficult to prove a primary origin. Elimination of the above 3 lesions (locations) decreases the incidence to between 0.2% and 2%. The major tumors found in order of frequency of occurrence are adenocarcinoma, carcinoid and leiomyosarcoma. Other extremely rare sarcomas are rhabdomyosarcoma, liposarcoma, angiosarcoma, fibrosarcoma, and neurogenic sarcomas. Adenocarcinomas account for approximately 50% of all cancers; then come carcinoids, approximately 35%; and leiomyosarcomas approximately 15%. The other rare sarcomas are all cumulatively under 0.5%. A table shows the distribution of these tumors. Malignant lesions are divided evenly between males and females. Greatest incidence with regard to age is as shown in a second table. The relative immunity of the small bowel to the development of malignant tumors is an enigma. Rapid transit time and fluid alkalinity may decrease bowel exposure time to carcinogens; or perhaps enzymes, such as certain of the hydrolases present in large quantities in the small bowel, may degrade some carcinogens. The high concentration of immunoglobulin A in the small bowel, may also help to decrease the incidence. Whatever the cause, this relatively rare state limits one's suspicion of this as a primary lesion, and by the time of diagnosis, the prognosis is poor.