Introduction:
Ovary is a common site of primary tumors and metastases. Metastases consist approximately 20% of ovarian cancers. Clinical symptoms of metastases may imitate symptoms of primary ovarian cancer. Metastatic tumors to the ovary in about 50%–80% of cases are bilateral. The 5-year survival rate is in the range of 10%–24%. It is rare not to localize the primary site.

Aim:
A case of giant metastatic ovarian tumor of unknown primary site in 61-year-old multipara was presented.

Material and methods:
The case was presented on the basis of medical record of the patient.

Case study:
A female with an abdominal mass was admitted to the Department of Gynecology for a surgical removal of the tumor. The patient complained of abdominal distension. She was qualified for a surgical procedure. During surgery a 24-cm tumor of the left ovary was resected. The intraoperative pathologic examination identified cystadenocarcinoma mucinosum. Surgical resection was extended and hysterectomy with right salpingo-oophorectomy and pelvic lymphadenectomy was performed. The pathologic examination reported that the tumor was compatible with Adenocarcinoma metastaticum et intestino crasso. Diagnostic imaging and endoscopy did not reveal a primary site. Two years after the surgery the patient feels well.

Results and discussion:
In pathologic examination there was a difficulty in determining the primary site. Final diagnosis was made based on immunohistochemical results. Immunohistochemical profile: CK7(–), CA125(–), CK20(+++), CDX2 (+++), Mucicarmine(7), is characteristic of colorectal cancer. Metastatic ovarian tumors require extended diagnostic imaging and histopathology.

Conclusions:
In preoperative diagnosis of ovarian tumors possibility of metastases should be taken into account. Diagnostic difficulties require close collaboration between the clinician and the pathologist at each stage of cancer diagnosis.