Metastasis is the process by which malignant cancer cells from a primary tumor spread to another site. In this process, tumor cells are shed from the primary tumor and move into blood or lymphatic vessels. The tumor cells are transported to other areas in the body where they invade other tissues. The NCI reports that the lungs, bones, liver, and brain are the most common sites of metastasis. Although it is rare, lymphomas can transform into malignant tumors and metastasize, or spread to other organs not in the lymphatic system. 

Metastatic Lymphoma

Simply because the term is not often used in lymphomas does not mean that lymphomas cannot metastasize. They can and often do spread to distant sites in the body if not controlled or caught early. However, when other cancers metastasize it normally means the cancer has formed a new secondary tumor in a new site. Since solid tumors aren't really an aspect of lymphoma and they are certainly not an aspect of leukemia, the notion of metastatic lymphoma becomes a little more complicated.

That said, on the rare occasion of metastatic lymphoma and that a lymphoma forms a distant tumor in the body, that tumor is most often found in the lungs, spleen, or the central nervous system.

B Cell Lymphoma occurs when B Cells mutate and become cancerous. Subsequently, as the cancerous B Cells clone themselves, the cancer proliferates.

Types of B cell lymphoma

Lymphomas are categorized according to how the B cells are affected. 

Follicular lymphoma

Burkitt's lymphoma

Endemic Burkitt's lymphoma

Sporadic Burkitt's lymphoma

Marginal Zone Lymphoma

Mucosa-Associated Lymphoid Tissue

MALT / MALToma (extranodal)

Monocytoid B cell lymphoma (nodal)

Splenic Lymphoma with villous lymphocytes

Mantle Cell Lymphoma

Large Cell Lymphoma

Diffuse Large Cell

Diffuse Mixed Cell

Immunoblastic Lymphoma

Primary Mediastinal B Cell Lymphoma

Angiocentric Lymphoma - Pulmonary B Cell

Chronic Lymphocytic Leukemia (CLL)

Small Lymphocytic Lymphoma (SLL)

Precursor B-lymphoblastic lymphoma

As a systemic disease, the term "metastasis" is typically not used in the conventional sense to describe the potential spread of lymphoma. Lymphoma and leukemia can disseminate throughout the body and there is evidence to suggest that the sites involved are related to what adhesion molecules and other targeting molecules are expressed on the lymphoma cells.  The following article may be a good starting point for what you are looking for: http://www.ncbi.nlm.nih.gov/pubmed/8980612

This is with my little knowledge I am writing. Even I support the view of Hung Luu. The word metastasis is not used in lymphoma. In leukemia and lymphoma, blood cells are becoming malignant . And it will be circulating in blood . In non Hodgkin s lymphoma, it affects Accessory lymphatic tissues in different parts of the body. Some text books say that lymphoma in later stages can become leukemia as more malignant cells circulAte in blood and leukemia can become lymphoma as the malignant blood cells get lodged in lymph nodes. 

The term metastasis is not usually used in lymphomas due to modification of the staging. In general the metastasis is the process by which malignant cancer cells from a primary tumor spread to another site.  The tumor cells are shed from the primary tumor and move into blood or lymphatic vessels. The malignant cells are transported to other areas in the body where they invade other tissues. The lymphomas can transform or infiltrate into malignant tumors and metastasize (CNS infiltration or metastasis), or spread to other organs not in the lymphatic system (Lung  metastasis ).

Thank you for your replies! 

I understand that metastasis is not the best word to describe lymphoma dissemination, but I am mainly interested in the mechanisms that underly this spread of malignant cells in and outside the lymphatic system.

Julie:

Excellent question! Here are my thoughts, based on some recent research:

Although not as common as the term "extranodal" (solely meaning organ or viscera outside the lymph system), the term metastasis is nonetheless legitimate in discussions of lymphoma and a search of the major medical databases I typically mine in my systematic reviews - including PUBMED/MEDLINE, Cochrane Library/Register, EMBASE, AMED, CINAHL, ISI Web of Science (WoS), BIOSIS, LILACS , ASSIA, and NHS SCEH - returns hundreds of references to metastatic lymphoma(s), and even to 100+ to precisely that expression in the title (and some to, more specifically, metastatic B-Cell Lymphoma). And note that besides well-known CNS metastasis (especially leptomeningeal), B-cell lymphomas have been documented to develop orbital/vitreous metastases, and metastases to the lung, liver, bone, GI system (especially stomach), as well as cardiac metastases, among several others (even, rarely, to the breast, as breast lymphoma).

As to the mode of metastatic migration for specifically B-cell lymphomas, preclinical studies have shown that lymphoma metastases preferentially spread through the lymphatic route, via tumor-draining lymph nodes (TDLNs), which can be accompanied by increased hematogenous spread to the spleen. In particular, B cells residing in these TDLNs stimulate lymphangiogenesis (thus implicating members of the VEGF family of growth factors as key mediators of lymphangiogenesis) and increase lymph flow, which promotes metastasis by physically increasing cell trafficking through the lymphatic drainage1,2. Thus, B-cell accumulation in tumor-draining lymph nodes (TDLNs) induces lymphangiogenesis (aka, lymphatic sinus growth) and elevates lymph flow to actively promote tumor dissemination through the lymphatic system.

Nor is it any longer thought that the lymphatic mode of dissemination is a passive one of simply providing a "conduit" path, but rather the lymphatic vasculature actually plays an active role in metastatic tumor spread, lymphangiogenic factors (especially VEGF-A and -C, and a tight network of chemokine receptors, with chemokine gradients favoring the entry of tumor cells into lymphatic vessels) essentially preparing a premetastatic niche conducive to establishment of secondary tumors, modulating tissue stroma within the draining lymph nodes, the secondary lymphoid organs, and other distant metastatic sites besides also in the primary tumor3-5.

I note one exciting development in the quest for lymphangiogenesis inhibitors is the potential for statins to behave as such lymphangiogenic blockers6, although we require mature clinical trials to move this into clinical practice.

References