B cells carry the same DNA as all other cells. The difference between cell types is in what sections are functionally expressed (made into proteins that do thei

B cells carry the same DNA as all other cells. The difference between cell types is in what sections are functionally expressed (made into proteins that do their work). This is determined by a multitude of factors. Cancer cells typically have mutations, even just single base pair changes, which change the way that genes are expressed in the cell and thereby influence such behavior. The original functions of the B cell aren't necessarily needed for other cell types to exhibit similar functions. The base plan is there, it just needs a nudge.