There is some general confusion about the similarities and differences between leukemia and lymphoma, the two main so-called blood cancers. As blood cancers, they are set apart from the other broad category of cancer, solid tumor cancers. However, this is misleading, since it is possible to develop tumors in lymphoma.
The best place to go for an answer to the question of what the difference between leukemia and lymphoma is the American Joint Committee on Cancer, or AJCC. This oversight body annually publishes the standards to be applied in staging every type of cancer in the United States, and its influence typically reaches well beyond the US.
The Cancer Staging Handbook
According to the AJCC's most recent publication (the seventh edition of the Cancer Staging Handbook), any cancer that affects the lymphoid cells—lymphoblast, lymphocyte, follicle center cell, immunoblast, plasma cell—should first be described as a Lymphoid Neoplasm. From there, the question on the difference between leukemia and lymphoma becomes one of disease presentation.
- If the disease only tends to affect circulating cells, it is considered a leukemia.
- If the disease tends to produce tumor masses, it is considered a lymphoma.
- If the disease presents both in the circulating cells and in a tumor mass, it is considered a lymphoma/leukemia.
The reason for this is because emerging research suggests there may not be a difference between leukemia and lymphoma; rather, they may be the same diseases in different stages. A good example is in chronic lymphocytic leukemia/small lymphocytic lymphoma (SLL/CLL), which had been considered different diseases but are now considered the same disease.