Lactating Adenoma Arising From Ovarian Mature Teratoma: An Unusual Presentation of a Young Pregnant Woman

Mature teratoma is a benign germ cell tumor, histologically comprising components from mesoderm, ectoderm, and endoderm layer tissue. Here, we report a rare case of lactating adenoma arising from mature teratoma of the ovary in a pregnant female. To the best of our knowledge, only four cases of lactating adenoma arising from ovarian teratoma have been reported in the literature so far. This case is the fifth case reported worldwide, and the first case report with dual rare findings - choroidal plexus and lactating adenoma of mammary tissue in benign mature cystic teratoma. This is the second case report which uses immunohistochemical (IHC) markers to confirm the diagnosis. Grossly, the cystic structure was measuring 10x7x5cm. The cut surface revealed mixed solid and cystic areas filled with pultaceous material admixed with hair. Microscopy showed an ovarian cyst lined by stratified squamous epithelium with underlying sebaceous glands, apocrine acini, fatty tissue, smooth muscle, and glial tissues. Also noted mammary tissue composed of proliferating hyperplastic acini with central dilated ducts filled with eosinophilic secretions arranged in lobules. Immunohistochemistry with estrogen receptor (ER) and progesterone receptor (PR) showed luminal and ductal positivity. Strong expression of IHC markers such as p63 and pan-cytokeratin (pan-CK) was noted in myoepithelial cells and luminal cells respectively. Thus, confirming it as mammary tissue with hyperplastic ducts and acini.