Before the present case, a total of four reported cases of duodenal collision tumor were found in the MedLine-listed literature. Our literature review has purposely been limited to collision tumors of duodenum excluding those from colorectal, gastric, appendiceal and other parts of the gastrointestinal tracts. The clinicopathologic features of these cases are summarized in .8–11
Clinicopathologic features of current and previous reported collision tumor in duodenum.
Conventional explorations usually do not confirm the coexistence of both tumors, as these findings are frequently made incidentally during histopathologic examination of the specimen. Given their extreme rarity in this location and the nature of collision tumors, it is of certain diagnostic benefit to extensively examine and section the tumor for histologic evaluation, and distinguish collision tumor from the more commonly encountered neoplasms demonstrating heterologous differentiated elements or mixed elements.
Indeed, this case could easily have been mis-considered as an adenocarcinoma with neuroendocrine features given the rarity of collision tumors in this location, and one may even completely miss the concurrent distinct and independent neuroendocrine tumor component, especially if only a limited examination and sectioning of the tumor are performed for histologic evaluation.
Two main features that are important in the diagnosis of collision tumor rather than neoplasms demonstrating mixed elements include: i) two distinctive and spatially independent tumor components macroscopically in the same location, and ii) demarcated morphology and immuno-expression patterns among the two tumors microscopically. Morphological and immunohistochemical examinations will show that the two components have a clear-cut distinction, and they have no intervening intermediate cell population.
Clinical implications of this condition and the mechanism responsible for the tumor formation of such an unusual constellation remain unclear. Mutual factors of carcinogenic initiation or progression for either tumor component can be speculated upon, but are unknown. In addition, the collision tumor encountered provided us with the curiosity finding of simultaneous and apparently independent lymphatic metastatic progression mechanisms, too. Since this is apparently the first such case of collision tumor arising in the third portion of duodenum, further study of additional cases and additional long-term follow-up will likely be necessary to better understand the clinical behavior of such tumors occurring in this unusual location. We suspect that the recurrence risk of the tumor encountered will most likely be primarily influenced by the biologic behavior of the more aggressive component, i.e. the duodenal adenocarcinoma. Nevertheless, having identified two separate invasive neoplastic processes will have an influence on postoperative treatment and follow-up decisions.