  Acute lymphoblastic leukemia (ALL) and chronic lymphocytic leukemia (CLL) are
two major forms of leukemia that arise from lymphoid cells (LCs). ALL occurs
mostly in children and CLL occurs mainly in old people. However, the
Philadelphia-chromosome-positive ALL (Ph+-ALL) and the Ph-like ALL occur in
both children and adults. To understand childhood leukemia/lymphoma, we have
recently proposed two hypotheses on the causes and the mechanism of cell
transformation of a LC. Hypothesis A is: repeated bone-remodeling during
bone-growth and bone-repair may be a source of cell injuries of marrow cells
including hematopoietic stem cells (HSCs), myeloid cells, and LCs. Hypothesis B
is: a LC may have three pathways on transformation: a slow, a rapid, and an
accelerated. We discuss in the present paper the developing mechanisms of ALL
and CLL by these hypotheses. Having a peak incidence in young children, ALL may
develop mainly as a result of rapid cell transformation of a lymphoblast (or
pro-lymphocyte). Differently, Ph+-ALL and Ph-like ALL may develop as results of
transformation of a lymphoblast via accelerated pathway. Occurring mainly in
adults, CLL may be a result of transformation of a memory B-cell via slow
pathway. By causing cell injuries of HSCs and LCs, repeated bone-remodeling
during bone-growth and bone-repair may be related to the cell transformation of
a LC. In conclusion, ALL may develop as a result of cell transformation of a
lymphoblast via rapid or accelerated pathway; and repeated bone-remodeling
during bone-growth may be a trigger for the cell transformation of a
lymphoblast in a child.
