Metastatic Malignancies to the Ovaries: Often Hiding in Plain Sight.

CONTEXT.—: Between 5% and 30% of malignant neoplasms involving the ovary are metastatic. A variety of neoplasms can metastasize to the ovary, including those from the colorectum, endometrium, breast, appendix, stomach, and cervix.

OBJECTIVE.—: To summarize the clinical, gross, and histologic features that aid in distinguishing primary ovarian neoplasms from metastatic neoplasms. Additionally, to discuss the immunohistochemical features that help identify the primary site of origin.

DATA SOURCES.—: Sources include literature review and cases identified from the authors' practice.

CONCLUSIONS.—: There are many features that can help distinguish a primary ovarian neoplasm from a metastatic lesion. The patient's clinical symptoms and history may suggest the primary site. On radiology, the absence of ascites is suggestive of metastasis. Laboratory tests such as cancer antigen 125 (CA 125) and carcinoembryonic antigen (CEA) are helpful in distinguishing a primary versus metastatic neoplasm. Gross features that favor metastasis are bilaterality and small tumor size. Metastatic lesions often have multinodular growth and involve the surface or superficial cortex. Histologic features favoring metastasis include a nodular or infiltrative pattern, stromal desmoplasia, hilar involvement, lymphovascular invasion, and an absence of benign or borderline components. The presence of extracellular mucin and signet ring cells also suggests metastasis. Distinct histologic features can be suggestive of the primary site. Immunohistochemical stains, such as cytokeratin (CK) 7, CK20, SATB homeobox 2 (SATB2), p16, paired box 8 (PAX8), WT1 transcription factor (WT1), estrogen receptor (ER), progesterone receptor (PR), and GATA-binding protein 3 (GATA3), can also be useful in evaluating the site of origin. Distinguishing between a primary ovarian tumor and metastasis is critical for determining prognosis and treatment.