Microscopic appearance of resected tumor. (A) Left ovary: Numerous signet-ring cells with pale cytoplasm are distributed singly or in nests in a luteinized stroma (hematoxylin-eosin stain, ×400). (B) Gastric biopsy: The lamina propria contains individually infiltrating, discohesive, poorly differentiated adenocarcinoma cells (hematoxylin-eosin stain, ×400). (C) Immunostain for β-hCG demonstrates strong diffuse cytoplasmic and membranous staining within the malignant cells (immunoperoxidase technique with DAB chromogen, ×400). (D) Immunostain for cytokeratin 7: The malignant cells are strongly immunopositive (immunoperoxidase technique with DAB chromogen, ×400) cell tissue from left ovarian cyst wall.