A national population-based study provides insight in the origin of malignancies metastatic to the ovary.

A significant proportion of ovarian malignancies consists of metastatic tumors, with a wide variety in site of origin. Differentiating between a primary and metastatic malignancy of the ovaries can be difficult and misdiagnosis might have considerable impact on both treatment and prognosis. To further examine the origin of malignancies metastatic to the ovary, we performed a large-scale, nationwide search for ovarian metastases in the Dutch Pathology Registry (PALGA). All pathology reports concerning malignancies metastatic to the ovary and associated primary tumors in the Netherlands between 2000 and 2010 were collected. Age, year of diagnosis, tumor type, location of the primary tumor, and side of the ovarian tumor were extracted from the database. We identified 2312 patients fulfilling our selection criteria. The most common primary malignancy sites were colon (33.2%), endometrium (17.1%), breast (14.3%), appendix (7.3%), and stomach (4.5%). The metastases were most frequently bilateral (46.3%) followed by unilateral metastases in the right (26.7%) and left ovary (19.8%), while side was unknown in 7.2% of cases. Of colorectal carcinomas, only 40.2% metastasized bilaterally, compared to 63.9% of breast, 62.9% of gastric, and 58.9% of appendix carcinomas. Left-sided colorectal carcinomas most often metastasized to the left ovary (p < 0.0001). We found colon carcinomas to be most frequently responsible for metastases to the ovaries, followed by endometrial and breast carcinomas. Metastases from breast, stomach, and appendix carcinomas were mostly bilateral, whereas metastases from colorectal carcinomas were mostly unilateral. The mechanisms underlying preferred sites for metastasis or side remain unclear.