Metastatic tumors account for up to 15 % of ovarian malignancies in western countries [1, 2] and may present a significant diagnostic challenge during intraoperative frozen section consultation. The primary site is most commonly located in the gastrointestinal tract, with approximately 30 % of cases originating from the colon, followed by appendiceal, gastric, and pancreatobiliary primaries [3, 4]. Among non-gastrointestinal primaries, breast cancer is the most frequent source of ovarian metastases [3, 5], which may also be an incidental finding in prophylactic or therapeutic oophorectomy specimens. Metastatic endometrial and cervical carcinomas to the ovary occur at a lower frequency and generally have less severe implications on the intraoperative management at the time of frozen section compared to other metastatic sites. While comprehensive surgical staging is typically performed for primary ovarian malignancies, gynecologic staging surgery is unnecessary for extragenital primary tumors metastatic to the ovary. Intraoperative frozen section evaluation plays a critical role in this distinction and therefore guides the extent of surgery.

The most important first step in assessing the origin of tumor—primary versus metastatic—is thorough review of the patient’s clinical history. However, the primary tumor may be occult and the metastasis may precede the diagnosis of primary tumor. In one study, 51 % of ovarian metastases of gastrointestinal origin were diagnosed prior to the discovery of the primary tumor [3]. The median age of patients with ovarian metastases is 53–55 years [4, 5], although patients with Krukenberg tumor typically present earlier (average age: 45 years) [6]. The clinical presentation may be similar to primary ovarian tumors—pelvic pain and mass effect, and rarely even hormonal (androgenic or estrogenic) manifestations, due to functioning stroma [6]. The macroscopic features may be helpful, as bilaterality, tumor size under 10 cm, ovarian surface involvement, and multinodular growth pattern are more common in metastatic tumors [7]; however, exceptions do occur. On microscopic examination, extensive lymphovascular invasion and ovarian hilus involvement are generally in favor of metastatic carcinoma. Comparison with the patient’s known primary should be made if the prior specimen is available at the time of frozen section, although the histological features at the metastatic site may slightly be different from those of the primary tumor. For example, mucinous tumors metastatic to the ovary may demonstrate a “maturation phenomenon,” mimicking a primary benign or borderline ovarian mucinous tumor [8]. Cystic growth pattern may be encountered in the ovarian metastasis, even when the primary tumor is predominantly solid [6].

The frozen section diagnosis—especially in difficult or equivocal cases—should not be made in isolation without intraoperative discussion with the surgeon. If only one ovary is received for frozen section, the surgeon should be inquired about the appearance of the other ovary and about the possibility of bilaterality, especially if dealing with a mucinous tumor. If a metastasis is suspected, intraoperative surgical evaluation of the pelvis and abdomen and sampling from any additional pelvic or intra-abdominal—intestinal, appendiceal, or gastric—lesions or enlarged intra-abdominal lymph nodes may be helpful. Intraoperative identification of pseudomyxoma peritonei by the surgeon or presence of extracellular mucinous material on the ovarian surfaces strongly favors appendiceal primary. Appendectomy is usually performed in this scenario even if the appendix appears grossly unremarkable.

Metastases to other gynecologic organs occur less commonly and may involve vagina, vulva, uterine cervix, endometrium, and fallopian tube—in decreasing order of frequency [5]. Metastatic tumors may mimic primaries at these sites and may be easily misinterpreted, especially due to their rare occurrence. Unusual morphologic features—e.g., intestinal-type differentiation with goblet cells or extensive lymphovascular invasion—should raise suspicion for a possible metastatic origin.

This chapter summarizes the clinical, gross, and microscopic features and site-specific key intraoperative consultation issues of the most common metastatic tumors—intestinal, signet-ring cell, pancreatobiliary and appendiceal adenocarcinomas, and breast and gynecologic primaries—involving the ovary. Metastases from other primary sites—lung, urinary tract, melanoma, and sarcomas—occur rarely, and their clinical and histopathologic features depend largely on the primary tumor site.