Malignant ovarian neoplasm is one of the most lethal malignancies among cancers of the female reproductive system. Occasionally, these tumors originate from non-ovarian organs as metastatic lesions since the ovary is a frequent metastatic target of many cancers. However, there limited clinical information on metastatic ovarian carcinoma (MOC) and its hallmarks are unknown. During the period of 1986-2015, 4,284 patients with malignant ovarian neoplasm were identified using the Tokai Ovarian Tumor Study Group (TOTSG) database. Of these, excluding borderline malignant tumor, 3,478 patients with malignant ovarian cancer were extracted. The pathological slides were evaluated under central pathological review. Among them, a total of 143 (4.1%) patients with MOC were identified. The median age of patients with MOC was 54 (29-82) years. The most and second most frequent original tumors were colorectal (43%, N=62) and gastric (29%, N=42) carcinoma, respectively. The rates of carcinoma of the appendix, breast, and pancreas were 8, 6, and 4%, respectively. This is the one of the largest studies clarifying the rates of MOC among malignant ovarian neoplasms. Although the rate is low, we should keep in mind that MOC, particularly from colorectal and gastric cancer should be considered when encountering clinical practice of ovarian cancer.
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