A 57-year-old woman visited our outpatient clinic complaining of poor appetite abdominal discomfort nausea and bloody stool for the past two weeks. Laboratory examination revealed anemia, with Hemoglobin level of 11.1 g/dl, HCT of 32.7%. The white blood cells and the platelet count were within normal limits. The blood chemistry profile showed nothing of note. However, her tumor markers were abnormal; Alpha-fetoprotein (AFP) was 1319 ng/ml (normal (Figure 1). There was a tumor near the hepatic flexure, with extramural extension. There was no distant metastasis. Subsequently, right hemicolectomy and lymph node dissection was then performed. The tumor was adhered to the duodenum and pancreas. Dissection was performed with somewhat difficult. There was no metastasis in the liver. Her Serum level of AFP was 370 ng/ml 9days after surgery. Port a tube was installed, unfortunately, she went to a medical center for further therapy.

Histopathology

The postoperative specimen consisted of a segment of colon attached with an appendix. On opening, there was a fungating tumor with central ulceration; measuring 4x3x2 cm, four cm from the proximal resection margin (Figure 2). The tumor was grayish white in color, and apparently has invaded through the muscle layer to the serosa. Viewing from the back side, the serosa appeared hemorrhagic with fibrous adhesive bands, indicating adhesion to the adjacent organs. Sections from the tumor displayed a polymorphous appearance, i.e. the tumor was composed of solid sheets with areas of glandular or papillary structure (Figure 3). The solid sheets consist of closely packed cells with eosinophilic or clear cytoplasm. In addition, they exhibited a variety of other patterns characteristic for YST: clear cell, hepatoid and reticular microcystic. A few Schiller-Duval bodies were observed (Figure 4). Immunochemical staining (IHCs) (Figure 5) showed the following results: HepPar 1 3+, diffuse; Glypican-3+, focal; AFP 3+, focal; CDX-3 +, diffuse. HCG was negative (not shown). Histological evaluation, in conjunction with IHC studies, we made this case as yolk sac tumor. Because the tumor invaded through the visceral peritoneum, with six lymph nodes positive out of seventeen examined. There was no radiological evidence of distant metastasis. This tumor was staged as pT4aN2a. Later, we submitted the whole tumor for histological examination, no conventional adenocarcinoma or choriocarcinoma components were found which led us to diagnose this tumor as pure yolk sac tumor of the colon.

DISCUSSION AND LITERATURE REVIEW

AFP-GC accounts for the majority of AFP-producing cancers. AFP-GC is considered as the subtype of gastric cancer, because it has propensity to metastasize to the liver and lymph node, resulting in poor prognosis. AFP-CRC behaves aggressively, similar to that of AFP-GC. The cellular and molecular mechanism responsible for their poor prognosis was not clearly understood. An early report indicated that AFP had a suppressive effect on lymphocyte transformation [8]. Another report indicated that AFP could enhance proliferative activity and increase angiogenesis due to positive expression of vascular endothelial growth factor VEGF [9]. In a study in 2000, Amemiya [10] found that hepatocyte growth factor (HGF) and c-met expression was higher in AFP-GC than that in AFP negative gastric cancer. Through the HGF and c-met pathway, tumor growth was promoted. Patients with AFP-CRC behaved poorly similar to patients with AFP-GC, perhaps through the same mechanism. AFP-CRC is extremely rare, since Nakajima et al, reported the first case of AFP-CRC in 1985 [11], only a few cases have been sporadically published in the literature [12], the largest series was from Ren [13]. They analyzed 20 patients on clinicopathological features and prognosis. None of their cases had yolk sac tumor. According to Otani [14], only four cases of colorectal adenocarcinoma with YST component have been reported in the English literature up to 2022, but they were traditional adenocarcinoma combined with YST, or with YST and choriocarcinoma. To the best of our knowledge, our present case is the first report of pure colonic YST.

It is worth mentioning that endodermal sinus and yolk sac tumor are used interchangeably. The pathogenesis of the yolk sac tumor in the colon cancer still remains unknown. One theory proposed a retrodifferention mechanism of mature cells into primitive pluripotent cells [15]. A case report by Otani [14] supported this theory. In their patient, the cells from the original adenocarcinoma and yolk sac tumor in the recurrence shared mutation in APC and TP53 genes. The second theory was that of the migration misplacement. During embryogenesis, the primitive gonadal cells migrated from the cranial cavity to the external genitalia. During their migration, some primitive germ cell might misplace at the migration pathway. These cells could transform into germ cell tumor [15]. Currently, there is no standard guideline to treat AFP-CRC patients with germ cell component. In the literature, they were usually treated according to traditional adenocarcinoma, receiving adjuvant chemotherapy after resection. It was promising that some patients could benefit from preoperative chemotherapy [16-20].

CONCLUSION

In conclusion, we reported the first case of pure yolk sac tumor in colon, in which primary tumor resection and lymph dissection were performed. It was unfortunate that our patient was transferred to a medical center for further therapy. We missed the opportunity to gain the knowledge about treating pure yolk sac tumor of the colon.