Testicular relapse of acute lymphoblastic leukemia (ALL)

Several aspects of acute lymphoblastic leukemia (ALL) converge towards the testis: (1) the overall prognosis is worse for boys than for girls; (2) the testis is a more frequent site of relapse of ALL than other organs; (3) age over 10 years (coinciding with the start of pubertal activation) is a recognized "high risk" background factor; (4) occult testicular relapse of ALL seems to be common. The underlying mechanisms behind these observations are discussed. If immunological defence mechanisms are important for the rejection of ALL cells from the body, the immunological tolerance of the testicular microenvironment might favour growth of ALL cells. Alternatively, the presence of specific growth promoting factors in the testis might enhance tumour cell proliferation. In this context, the newly discovered presence of a lymphocyte growth factor (interleukin-1-like, IL-1) at high concentrations in the testis of several mammals, including man, is of great interest. As this factor seems to be under hormonal control, in future it may offer opportunities to influence the tendency to testicular involvement, and thus prognosis, in ALL.