PMC5126084_01
Radiographic findings. (A) CT image of the lower abdomen showing a poorly delineated, partially necrotic tumor in the ileocecal region with a maximum diameter of 9.6 cm. (B) CT scan of the upper abdomen demonstrating hepatic metastases in segments II, VII, and VIII with a maximum diameter of 2.6 cm (segment VI not visible in this image plane). (C) Follow-up examination 24 months later showing subtotal regression of the metastases in segments VII and VIII and total regression of the lesion in segment II.
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F1
Computed tomography (CT) imaging confirmed the diagnosis of a 9.6-cm cecal mass (Figure 1A) and identified four hepatic metastases with a maximum diameter of 2.6 cm (Figure 1B). Third line therapy with five cycles of carboplatin and bleomycin was initiated, leading to stabilization of disease (Figure 1C).
Macroscopic and histopathological images. (A) Gross images showing a hemorrhagic and partially necrotic tumor with transmural infiltration of the colonic wall. (B) Histologic images showing a dimorphic population of syncytiotrophoblastic giant cells (arrows) and mononucleate trophoblastic cells arranged in a plexiform pattern invading the colonic wall with extensive hemorrhagic necrosis (left, 100x). Trophoblastic cells have ample eosinophilic cytoplasm and show markedly atypical nuclei with irregular nuclear membranes, coarse chromatin, and a single, prominent nucleolus. Syncytiotrophoblastic cells (arrows) have multiple nuclei with variable size and abundant eosinophilic to amphiphilic cytoplasm (right, 250x). Cytoplasmic vacuolization and lacunae are frequently observed.
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F2
Gross examination of the resection specimen showed a poorly marginated tumor localized to the cecum and terminal ileum with serosal perforation (Figure 2A). Histopathological analysis revealed a solid carcinoma consisting of a dimorphic population of syncytiotrophoblastic giant cells and mononucleate trophoblastic cells arranged in a plexiform pattern with transmural infiltration of the colonic wall (Figure 2B) and multifocal venous invasion.
Protein expression profiling by immunohistochemistry. Immunohistochemical stains (from left to right, top to bottom) showing diffuse, strong cytoplasmic reactivity of the neoplastic cell population for pan-CK. beta-HCG stain highlights syncytiotrophoblastic giant cells (all 400x). No expression of CDX2 was observed in the tumor cells; note the normal colonic epithelium in the upper left corner (40x). Analysis of postulated oncogenes revealed strong overexpression of p53, c-MYC, and p16. The neoplastic cell population showed an isolated loss of PMS2, while MLH1 was maintained; note the positively stained tumor infiltrating lymphocytes (all 400x).
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F3
Immunohistochemical analysis demonstrated strong, diffuse cytoplasmic reactivity for pan-cytokeratin (pan-CK) and beta-HCG, while stains for the intestinal transcription factor CDX2 were negative (Figure 3, top). Immunohistochemical analysis of the MMR proteins MLH1, PMS2, MSH6, and MSH2, showed an isolated loss of PMS2 protein (Figure 3, bottom right).