Leukemia and lymphoma?!
Question: Why is plasma cell malingnacy classified as leukemia but B cell malignancy classified as lymphoma?
Aren't plasma cells derived from B cell?
Answers: Why is plasma cell malingnacy classified as leukemia but B cell malignancy classified as lymphoma?
Aren't plasma cells derived from B cell?
Good questions...
B lymphocytes are in simple terms your antibody producing cells. Initially, they are immune surveillance cells, looking for their specific target (foreign protein, virus, bacteria, anything that is not you) that they were programmed to recognize. When found, they are stimulated and may become plasma cells (which are B cells but very mature, sophisticated ones), a committed cell to antibody production. Some can become memory cells, which are now smarter and will recognize a foreign attack more quickly next time (they remember, get it?).
Cancers that arise from B cells, can be either leukemia OR lymphoma. This is somewhat of an artificial construct, since there is considerable overlap. A very simple characteristic for leukemia would be that it is predominantly demonstrated in the blood and bone marrow. For lymphoma, you have predominant disease in the lymph nodes (you get masses). However, many leukemias can form masses, and many lymphomas can "spill over" into the bloodstream and give concomitant leukemia appearance as well.
Best wishes
As already stated, the difference between a lymphoma and a leukemia depends on what's involved (primarily lymph nodes/solid organs in the former, and the blood/marrow in the latter).
So, B cell malignancies can be a leukemia or lymphoma, depending on what is involved. Plasma cells, as you correctly pointed out, are a form of B cells (terminally differentiated). When they occur in solid organs, they're commonly not called lymphomas but rather known as multiple myeloma/plasmacytoma; they can also be in the blood and be called a leukemia.