A 70-year-old man was referred to our hospital for gastric cancer that was detected during screening by esophagogastroduodenoscopy (EGD).

No significant medical history was identified, except dysuria caused by bladder contraction.

Initial laboratory data showed a serum level of AFP of 32.3 ng/mL (normal range: 0-15 ng/mL), but no other abnormality, which included other tumor markers, such as, carcinoembryonic antigen (CEA) and carbohydrate antigen 19-9 (CA19-9).

EGD revealed a 5-cm ulcerofungating mass that was comprised of three septate ulcers in the greater curvature of the gastric antrum.

A pathological examination of endoscopic biopsy tissues confirmed the presence of moderately differentiated tubular adenocarcinoma.

Subsequent abdominopelvic computed tomography visualized a gastric mass with deep ulceration in the gastric antrum with perigastric lymph node enlargement.

No metastatic lesions were observed in the liver, lung or peritoneum, and chest radiography showed no significant findings.

Radical subtotal gastrectomy with D2 lymph node dissection and Billroth II gastrojejunostomy were performed.

Grossly, the resected specimen contained double lesions: the first was a 5.8 cm × 3.2 cm ulcerofungating mass in the antrum, with extensive hemorrhage and light gray fibrosis; and the second was a nearby 2.5 cm × 2.0 cm ulcerative lesion (Figure ​1).

Microscopically, massive numbers of pleomorphic, bizarre tumor cells with hemorrhage (syncytiotrophoblasts and cytotrophoblasts) were observed in the first lesion.

Hematoxylin and eosin (HE)-stained tissues revealed a bubbly purple cytoplasm and giant nuclei at a magnification of 40 × (Figure ​2A) and 100 × (Figure ​2B).

The tumor involved the proper muscle layer (T2a) and metastasis was found in four of 56 regional lymph nodes (N1).

Immunohistochemical staining showed positive immunoreactivity for β-human chorionic gonadotropin (HCG) (Figure ​3A) and focal positivity for AFP (Figure ​3B).

These findings confirmed the presence of gastric choriocarcinoma that contained small foci of an AFP-producing adenocarcinoma.

The second lesion was moderately differentiated tubular adenocarcinoma, which extended to the submucosal layer (T1b).

It was close to, but distinct from the first lesion, which was negative by immunohistochemical staining for β-HCG and AFP.

The patient had an uneventful postoperative course and was discharged on postoperative day 9.

Two weeks later, his HCG level was 176 mIU/mL (normal range: 0-10 mIU/mL) and his AFP level was 10.0 ng/mL.

Six cycles of adjuvant chemotherapy with capecitabine (Xeloda; Hoffmann-La Roche Inc., Nutley, NJ, USA) was started at 2500 mg/m2 per day for 14 d/cycle.

After two cycles, his β-HCG level had declined to < 3 mIU/mL, and has since remained at this level.

No recurrence or distant metastasis had occurred at his 4-year postoperative follow-up.