Context.-Splenic metastases from solid tumors, defined as parenchymal lesion, are considered exceptional. Nevertheless, the number of case reports has been increasing due to the improvement of imaging techniques and the long-term follow-up of patients with cancer. Splenic metastases occur in a context of multivisceral disseminated cancer or as a solitary lesion.

Objective.-To provide a general overview of the clini-copathologic features, differential diagnosis, and pathogenesis of splenic metastases.

Data Sources.-Relevant articles indexed in PubMed (National Library of Medicine) database. The search was based on the following terms: (metastasis or metastases) and spleen.

Conclusions.-The most common primary sources of splenic metastasis are breast, lung, colorectal, and ovarian carcinomas and melanoma in cases of multivisceral cancer and colorectal and ovarian carcinomas in cases of solitary splenic lesion. Splenectomy can be replaced by less aggressive methods such as fine-needle aspiration or percu-taneous biopsy for establishing the diagnosis of solitary splenic metastasis. The main differential diagnoses are primary lymphoma, vascular tumors, and infectious lesions of the spleen. The relative rarity of splenic metastases could be explained by anatomic factors and the inhibitory effect of the splenic microenvironment on the growth of meta-static cells. The analysis of clinical case reports suggests that solitary splenic metastases may result from the growth of an early blood-borne micrometastasis following a period of clinical latency, often several years after the diagnosis of the primary tumor.

Metastases from solid tumors to the spleen due to he-matogenous dissemination are confined to the splenic parenchyma and should not be confused with small superficial subcapsular foci associated with peritoneal dissemination observed in ovarian cancers.1 According to this definition, splenic metastases were thought to be exceptional, but the incidence of reported cases has been increasing due to the improvement of medical imaging and the long-term follow-up of patients with cancer. 2 Metastases to the spleen generally occur in a context of multivisceral metastatic cancer at terminal stage. Solitary metastases have also been reported.1-33 They are becoming a diagnostic dilemma with primary tumors of the spleen. This review outlines the clinical presentation, the diagnostic procedure, the pathologic features, the differential diagnosis, and the pathogenesis of splenic metastases.

CLINICAL PRESENTATION

The prevalence of splenic metastases in large populations with cancer was mainly obtained from autopsy series published before 1990 and ranged between 2.3% and 7.1%.34 The largest autopsy series was reported by Berge.34 He found 312 splenic metastases for 7165 autopsies performed for cancer. In his study, microscopic splenic metastases were identified in 50% of subjects who had metastases in at least 5 organs. After 1990, studies from different parts of the world brought indications about the prevalence of splenic metastases in living patients. In a Western study,35 1.3% of 1280 sequential tumors in sple-nectomy specimens were metastatic. In the same study, 9.8% of 122 splenectomies performed for diagnosis contained metastasis.35 In a Japanese study, 0.15% of 24 761 patients examined by ultrasonography had splenic metastasis. 3 A Chinese report found metastasis in 1.1% of 1743 sequential splenectomy specimens.36

Most splenic metastases are a part of multivisceral met-astatic disease. In this context, breast, lung, ovarian, colorectal, and gastric carcinomas and skin melanoma are the most common primary sources.34,36 Skin melanoma has the highest rate of splenic metastases per primary tumor because more than 30% of patients with skin melanoma have splenic metastasis at autopsy.33,34,36 Splenic metastases also occur as a solitary splenic mass, synchronous or me-tachronous to the primary tumor. To our knowledge, 93 well-documented cases of solitary splenic metastases have been reported to date (Table).3-32 The time from the diagnosis of primary tumor to the discovery of solitary splenic metastasis ranges from 0 to 264 months with a median of 28 months. Colorectal and ovarian carcinomas are the most common sources. On the other hand, solitary splenic metastases from breast carcinoma22-24 or skin melanoma33 are rare. Exceptionally, a splenic metastasis reveals a clinically occult primary tumor.17 Only 1 report described a solitary splenic metastasis from unknown primary.32

Splenic metastases are most often incidentally detected by ultrasonography or computed tomography scanning in the regular follow-up of patients with cancer or in the workup performed at the time of any event related to cancer. When isolated, more than 60% of splenic metastases are asymptomatic (Table). The increasing use of 18-fluo-rodeoxyglucose- positron emission tomography scanning has resulted in more patients with asymptomatic metastases being identified than previously found using conventional radiologic techniques.2 Splenic metastasis can also be revealed by fatigue,3 weight loss,5 fever,16 abdominal pain,* splenomegaly,5,25,32 anemia or thrombocytope-nia due to hypersplenism,14,16 and more rarely by splenic rupture.5,11,24 Serum level of tumor markers used in the follow-up of patients with cancer can predict the appearance of solitary splenic metastases before their clinical expression or radiologic detection and decreases to the normal range after splenectomy.