The caption on the chart at Todar's Online Textbook of Bacteriology, where I got this, reads, "Origin and differentiation of cells of the immune system."
And please note that it was Hannah, home schooling with the kids, not me, who happened to be leisurely browsing an article entitled "Immune Defense Against Bacterial Pathogens: Adaptive or Acquired Immunity."
Anyway, so this is what the "undifferentiated" in my "Undifferentiated Acute Leukemia" stands for.
Let me explain.
This chart shows how immune system cells "differentiate." They start as stem cells—hematopoietic, or blood stem cells, rather than infant stem cells, which can become any cell in the body—then split into either lymphoid or myeloid cells. These lymphoid cells become lymphocytes, the killers of the blood stream, and the myeloid cells become all those other cells listed in the chart.
The two major types of acute leukemia are Acute Lymphoid Leukemia (ALL) and Acute Myeloid Leukemia (AML).
The reason that my leukemia is "undifferentiated" is because my blood stem cells were stopping before they ever "diffentiated" into lymphoid or myeloid cells. Thus, my leukemia was neither ALL nor AML.
Final picture: What happens is that a blood cell stops developing, but then divides and forgets how to die when it's supposed to. This mutated cell, called a blast because it is not a fully grown cell (thus the word "Blastic" in Blastic Plasmacytoid Dendritic Cell Neoplasm), then proliferates through the bone marrow and blood stream, preventing normal development of other cells and normal operation of the blood and lymph system. Mine stop before they split into lymphoid or myeloid cells, while most leukemias run into the problem somewhere after that split.
I don't know how many of you are interested in that kind of thing, but it was a neat picture for me.
Good day to you!