The immunohistochemical profile, CDX2-positive, CK7-positive, TTF-1-negative and CK20-negative, produced a positive predictive value of 85.7% for signet-ring cell adenocarcinoma in a documented case of the cancer developing within a teratoma, underscoring the usefulness of immunohistochemical markers in determining the tissue of origin (29). The gene discussed is TTF1; the disease is signet ring cell carcinoma.