Krukenburg tumor is a metastatic malignancy of the ovary characterized by mucin-rich signet-ring adenocarcinoma that primarily arises from a gastrointestinal site in most cases and less commonly from other sites. Often these tumors are bilateral (over 80%), given its metastatic nature. This tumor is named after Friedrich Ernst Krukenberg (1871-1946), who reported a new type of ovarian malignancy in 1896. This was discovered to be metastatic in origin from primary gastrointestinal site 6 years later.
In most cases, the stomach has been attributed to be the primary site with studies showing this to be in about 70% of cases. Gastric and colorectal cancers collectively account for almost 90% of the primary site for this tumor. Other less common primary sites described in the literature are breast, appendix, small intestine, gallbladder, urinary bladder, biliary tract, pancreas, ampulla of Vater, or uterine cervix.
The average age of diagnosis is 45 years. However, it can be seen in all age groups. Of all the ovarian tumors diagnosed, Krukenburg tumors make up about 1% to 2% of these tumors. The incidence is higher in countries like Korea, Japan, and China where the tumor makes up about 20% of all ovarian cancers.
The exact mechanism of tumor spread is still unknown. The tumor is thought to spread via 1 of the 3 mechanisms: (1) the lymphatic system, (2) the hematogenous system, or (3) the transcoelomic pathway. Hematogenous and lymphatic pathway means the tumor spreads through blood vessels or lymphatic channel respectively. Transcoelomic pathway means the actual cancer cells directly spread through abdominal route to adjacent organs. Given the tumor is diagnosed at an advanced age, it is believed that the tumor metastasizes through mixed pathways. The average age of diagnosis co-relates to increased vascularity of the ovaries which supports the lymphatic and hematogenous spread hypothesis.
The lymphatic route is believed to be the most likely route of cancer spread with several supporting evidence:
Grossly, the ovaries are asymmetrically enlarged with a bosselated contour. They are usually solid, but can occasionally be cystic. The capsular surface is mostly free of any tumor infiltrates, adhesions, implants or deposits which can be deceptive and appear as a primary ovarian tumor.
The characteristic finding of this tumor is the presence of mucin-laden signet-ring cells, which is present in at least 10% of the cases. The diagnostic criteria of WHO based on Serov and Scully description are for making the diagnosis states:
Histochemically, the intracytoplasmic mucins of the signet-ring is neutral and acidic and stains with Mayer mucicarmine, periodic acid-Schiff with diastase digestion, and Alcian blue stain. Immunohistochemically, these tumors stain positive for cytokeratin (AE1/AE3), and epithelial membrane antigen and they stain negative for inhibin and vimentin.
These tumors can be asymptomatic or may manifest with non-specific gastrointestinal signs and symptoms as abdominal or pelvic pain, bloating, ascites, or dyspareunia. These tumors can become autonomous and produce hormones leading to vaginal bleeding, menstrual cycle irregularities, hirsutism, or rarely virilization.
Given the non-specific signs and symptoms, work-up involves obtaining imaging including computed tomography (CT) scan or ultrasound of the abdomen and pelvis. These tumors often appear as bilateral ovarian masses and usually appear solid but can also be cystic. Pre-operative level for serum CA-125 can be elevated and decreases after tumor resection. These levels can be used for:
No optimal treatment strategy for these tumors has been established. Radiation therapy has no significant role in the prognosis of patients with Krukenberg tumor. Similarly, chemotherapy has not demonstrated any benefits for these patients. Given the metastatic nature and lower rate of resectability, surgery is deferred as it does not offer any increased survival time. However, if the metastasis is primarily limited to ovaries, then surgery may offer increased survival time.
Classic Krukenberg tumors (i.e., tumors with signet ring cells that lack tubular formation) must be distinguished from ovarian tumors that contain signet ring cells with mucinous or nonmucinous material.
Ovarian tumors with mucin stain similar to Krukenberg tumor, but they also stain positive for chromogranin and synaptophysin which can differentiate them from Krukenberg tumor.
Ovarian tumor with signet ring cell without mucin are divided into signet-ring stromal tumor (benign, unilateral, devoid of epithelial differentiation, stain positive for vimentin and negative for cytokeratin), sclerosing stromal cell tumor (contain lipid with no reactivity to periodic acid-Schiff stain and stain positive for inhibin stain), and clear cell adenocarcinoma of the ovary (contains glycogen that stains with periodic acid-Schiff, papillary and tubulocystic pattern with hobnail cells).
Tubular Krukenberg tumors (i.e., cells arranged in tubules) must be distinguished from ovarian tumors with an annular or tubular pattern including Sertoli-Leydig cell tumor (lack of signet-ring cells, stain positive for inhibin and negative to cytokeratin), endometrioid carcinoma, and tumor of Wolffian origin.
Since Krukenberg tumor is a metastatic disease from the gastrointestinal site or other organs, it is classified as stage IV disease.
Given the bilateral and metastatic nature of this disease, prognosis remains poor. Patients usually die in 2 years with a median survival of 14 months reported in the literature.
Krukenberg tumor is a metastatic disease to the ovaries composed of mucin-rich signet-ring cells. The most common primary site for this tumor is the stomach. These tumors spread most likely through the lymphatic channels. Diagnosis of Krukenberg tumor involves careful radiological evaluation of gastrointestinal and other potential sites. With a known primary tumor, CA-125 levels can help with early detection of ovarian metastasis as well assist with prognosis and monitoring of this disease. Currently, no established treatment is available with extremely poor prognosis for this tumor.