The spleen is an organ situated beneath the rib cage on the left side of the abdomen. It performs dual roles in the body’s immune defense and blood maintenance. The spleen acts as a major hub for immune surveillance, housing white blood cells that fight infection. Additionally, it serves as a filter, removing old or damaged red blood cells. While the spleen is frequently involved in systemic diseases due to its high concentration of immune tissue, cancer that starts directly within the spleen is exceptionally rare.
Understanding Primary Versus Secondary Spleen Cancer
The term “spleen cancer” most often refers to a secondary malignancy, meaning the disease has spread to the spleen from a primary tumor located elsewhere. Secondary involvement is significantly more common than cancer originating in the organ itself. Cancers that frequently spread to the spleen include leukemias, lymphomas starting in other lymph nodes, and solid tumors such as those from the lung, breast, or melanoma.
The rarity of a primary tumor contrasts with the spleen’s frequent involvement in blood cancers, where malignant cells are carried through the bloodstream. Even for solid tumors, the spleen appears to resist metastatic colonization, a phenomenon sometimes termed the “spleen paradox.” This resistance is attributed to anatomical and functional characteristics, including the high density of anti-tumor immune cells and the unique structure of the splenic blood vessels.
The spleen’s sharp arterial angle and rhythmic contractions may make it mechanically difficult for circulating tumor cells to implant and grow. Furthermore, the absence of afferent lymphatic vessels, a common route for cancer spread in other organs, contributes to the spleen’s protection from non-hematological metastasis. This distinction between secondary involvement and true primary cancer is fundamental to understanding malignancy affecting the spleen.
Specific Etiologies of Primary Spleen Malignancies
Primary malignant tumors of the spleen are almost exclusively limited to two main types: Non-Hodgkin Lymphoma and Splenic Angiosarcoma. The causes for these two distinct malignancies are highly specific and involve different pathological mechanisms. Primary splenic lymphoma, the most common cancer originating in the spleen, arises from the organ’s lymphatic tissue.
A strong association exists between certain viral infections and the development of B-cell Non-Hodgkin Lymphomas in the spleen, particularly splenic marginal zone lymphoma. Chronic infection with the Hepatitis C virus (HCV) is a significant predisposing factor for this subtype. While the virus does not directly infect lymphocytes, its chronic presence causes continuous immune system stimulation, leading to uncontrolled B-cell proliferation and malignant transformation.
Other viral infections that compromise the immune system, such as the Human Immunodeficiency Virus (HIV) and Epstein-Barr Virus (EBV), also increase the risk of developing Non-Hodgkin Lymphoma in the spleen. The underlying theme is the sustained disruption of normal immune regulation, which creates an environment permissive for the transformation of white blood cells. These infectious agents represent the most defined external causes, though the exact genetic trigger for most cases remains unknown.
The second major primary malignancy, splenic angiosarcoma, is an exceedingly rare and aggressive cancer developing from the endothelial cells lining the spleen’s blood vessels. The causes for this tumor are often linked to specific occupational or historical environmental exposures. Exposure to certain chemicals is a known risk factor for angiosarcoma in various organs, including the spleen.
Historically, exposure to Thorotrast, a radioactive contrast agent used in medical imaging, is a recognized cause of angiosarcoma due to its long-term retention in the spleen and liver. Industrial exposure to vinyl chloride, used in PVC plastic production, and to arsenic compounds has also been linked to increased risk. These carcinogens induce DNA damage in the vascular lining cells, leading to malignant transformation.
Systemic Conditions That Increase Risk
Several systemic conditions and general factors increase the overall risk of developing cancers that may involve the spleen. Advanced age is a general risk factor for almost all cancers, with the majority of splenic malignancy cases diagnosed in individuals over fifty years old. This heightened susceptibility is due to the cumulative effect of cellular damage and a less efficient immune system over time.
Conditions causing chronic immune suppression significantly elevate the risk for lymphomas, the most common malignancy involving the spleen. Individuals requiring long-term immunosuppressive therapy after organ transplants, or those with chronic inflammatory diseases, face a higher likelihood of developing these cancers. This impaired immune function reduces the body’s ability to recognize and destroy abnormal cells.
Certain inherited or acquired genetic syndromes that predispose individuals to hematological disorders also increase the risk. People with underlying blood disorders like myeloproliferative neoplasms or polycythemia vera may experience abnormal cell growth that can progress to malignancy with splenic involvement. These systemic factors create a permissive environment for cancerous cells to proliferate, either by causing mutations or by preventing immune control.