[Secondary tumors of the gastrointestinal tract]

Metastatic involvement of the gastrointestinal tract is rare and may cause considerable difficulties with respect to differential diagnosis. The gastrointestinal tract may either be affected by direct invasion, intraperitoneal dissemination or hematogenous cancer spread, the latter most often originating from malignant melanoma, breast and lung carcinomas. Metastatic deposits primarily develop within the submucosa. Secondary involvement of the mucosa typically leads to centrally depressed and/or ulcerated (volcano-like) nodular lesions. In histology, lack of a mucosal in situ component favors diagnosis of metastasis, whereas presence of an adenomatous precursor lesion is regarded to be characteristic of primary tumors. This concept, however, has recently been challenged by demonstrating metastatic cancer growth along intact basement membranes within the mucosal layer, i.e. mucosal colonization. The histopathological, immunohistochemical and clinical features of secondary gastrointestinal tumors are discussed in detail, focusing on criteria for differential diagnosis. The prognosis of affected patients is generally poor.