Malignant small bowel tumors are extremely rare, accounting for 0.1% to 0.3% of all malignancies. Fewer than 2,400 new cases of small bowel malignancy are reported in the United States each year. Malignant tumors, which account for about two-thirds of all primary small bowel tumors, consist of four primary subtypes: adenocarcinoma, carcinoid tumor, lymphoma, and sarcoma (or gastrointestinal [GI] stromal tumor). Each malignancy is characterized by unique predisposing factors, anatomy, and biology. The prevalence, pattern, and relevance of both regional lymph node and distant metastases differ. As a result, the study of malignant small bowel tumors, taken as an aggregate, is fraught with difficulty.
Although retrospective data offer some insight into the natural history of this group of diseases, there are many limitations. Single-center reviews often describe experience spanning many decades, during which the spectrum of the disease must inevitably change (as, for example, refinements in imaging and improvements in treatment and treatment-related morbidity evolve). Large multi-institutional data sets such as the National Cancer Data Base are limited by internal consistency of data entry from multiple sources, details of treatment, and consistent long-term follow-up.
These sources of information are the best we have to define the demographics and natural history of these rare diseases. However, they cannot define the impact of any given treatment on outcome. This can only be accomplished by carefully controlled prospective trials. Given the rarity of these tumors and the enormous resources involved in the successful completion of such trials, it is unlikely that they will ever be conducted. Rather, many of our treatment paradigms will evolve as extrapolations from similar, more common tumors in other locations.
Alternatively, it is conceivable that we may be able to discern unique biologic susceptibilities of these tumors by genetic fingerprinting of individual tumors. At present, however, that possibility remains within the realm of medical speculation rather than reality.
It is against this background that Kummar and associates present a well-written, concise review of one of the more common small bowel malignancies, small bowel adenocarcinoma. The authors have included in their review adenocarcinoma of the duodenum, a site that accounts for over half of all small bowel adenocarcinomas. These tumors are often included in series reporting peripancreatic malignancy, although it appears clear that their biology is different, ie, consistent with other enteric tumors. Surgical resection—with either segmental duodenectomy or pancreaticoduodenectomy (depending on anatomic considerations)—is appropriate. Local resection is inadequate as it is associated with a high rate of subsequent local recurrence. As there is significant long-term survival in the setting of node-positive disease, regional lymphadenectomy in patients with this type of adenocarcinoma may, in fact, be therapeutic in some patients.
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