The term 'metastatic lymphoma' does not refer to a diagnosis. Unlike many of the subtypes of lymphoma we have featured in these articles, metastatic lymphoma is not one of them. While it is possible for a person's lymphoma to metastasize, or spread to distant sites of the body compared to where it began, it is not very common to discuss advanced lymphomas in terms of metastasis.
When we discuss cancer, we normally do so according to anatomy breast cancer, lung cancer, kidney cancer, etc. If it is determined that, for example, a case of cancer began in the lungs, then the lungs would be considered the primary site of that cancer, meaning the site of the cancer's origin.
If it is later determined that the lung cancer is not merely confined to the lung, but has in fact spread to local sites (in this case, perhaps somewhere in the chest) as well as distant sites, then it would be considered a case of metastatic lung cancer.
While some metastatic cancers can be treated, most often when a cancer has metastasized well beyond its primary origin, it is not treatable and is often fatal. In fact, when we read of people dying from cancer, it is because their cancer has metastasized.
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.
Sources: Leukemia & Lymphoma Society, National Cancer Institute, National Institutes of Health
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