FINAL DIAGNOSIS: Micropapillary carcinoma (non-invasive type) of the ovary associated with a mature cystic teratoma (dermoid cyst)
Micropapillary serous carcinoma (MPSC), which represents 6 - 18% of all serous borderline tumors, is a relatively rare neoplasm and represents a subset of borderline epithelial tumors of the ovary.1 On gross examination, MPSC are intracystic or exophytic with or without a cystic component, and exhibit prominent papillary excrescences.2 MPSC is characterized histologically by an exuberant proliferation of small, bland cells with high nuclear to cytoplasmic ratios that arise in a nonhierarchical fashion from large fibrotic, edematous or myxoid papillary stalks or from cyst walls. The proliferating cells form solid cribriform patterns or, more characteristically, complex filigree formations, dubbed "medusa head" for their likeness to the serpent-headed goddess of myth. By convention, the diagnosis of MPSC is made when the papillae are at least five times as long as they are wide, and the micropapillary architecture described is present in at least a continuous 5 mm section on a single slide.3,4
Ovarian surface epithelial tumors are divided into benign (tumors that lack exuberant cellular proliferation and invasive behavior), borderline (neoplasms that show exuberant cellular proliferation but no invasive behavior), and malignant (invasive tumors). According to this classification scheme, non-invasive serous tumors with a micropapillary architecture would be classified as borderline serous tumors. However, many consider these neoplasms to be low-grade carcinomas, thus the diagnosis "micropapillary carcinoma (non-invasive type)", since studies have shown noninvasive serous borderline tumors with a micropapillary pattern are more likely to be associated with invasive peritoneal implants, advanced stage at presentation, increased incidence of recurrence, and higher mortality rates than typical serous borderline tumors.4,5 Additionally, MPSC are more likely to be bilateral (up to 90% of cases).
In this case, we report an MPSC arising in association with a mature cystic teratoma. According to proposed molecular models of ovarian surface epithelial cancers, micropapillary carcinomas represent the intermediate stage in an "adenoma-borderline tumor-carcinoma" pathway.6 In addition, malignant neoplasms arising from mature cystic teratomas, which occurs in 0.2 - 1.4% of cases, are a result of malignant transformation of one of the benign components of the teratoma, such as squamous epithelium (squamous cell carcinoma), adnexal glands (adenocarcinoma), or cartilage (chondrosarcoma).7 Thus, the case presented most likely represents a collision tumor, in which a dermoid cyst of germ cell origin occurred incidentally adjacent to an MPSC of ovarian surface epithelial origin.
In conclusion, we describe an unusual presentation of a micropapillary serous carcinoma occurring in association with a mature cystic teratoma, highlighting the following points:
Contributed by Nicole N. Esposito, M.D. and Gregory J. Naus, M.D.