CK7+/CK20+/CDX2+ mucinous carcinoma, arising in a mature cystic teratoma of ovary, presenting with disseminated metastasis and pseudomyxoma peritonei.

Mucinous carcinomas arising within an ovarian dermoid tumor are rare. Most of the cases reported in the literature show morphological features resembling an appendiceal mucinous neoplasm. They exhibit CK7-/CK20+ immunophenotype similar to carcinomas of the lower gastrointestinal tract. In this report, we have described a case of a well-differentiated mucinous carcinoma arising within a mature cystic teratoma. The mucinous carcinoma showed a spectrum of morphological patterns, including cystadenoma-like areas, proliferative/borderline areas, villous adenoma-like areas, and areas of invasive carcinoma. In addition, our case showed some unusual findings, namely, diffuse CK7 positivity, associated pseudomyxoma peritonei, and metastasis to lungs. These features were not demonstrated in any of the previously reported cases. Our case shows that the teratomatous mucinous neoplasm of the ovary may show CK7+/CK20+/CDX2 + immunoprofile making it immunohistochemically indistinguishable from a primary ovarian mucinous neoplasm or a metastatic mucinous carcinoma of the lower gastrointestinal tract.