Adult T-cell leukemia complicated by hypercalcemia. Report of three autopsy cases with special reference to the etiologic factor of hypercalcemia.

Three autopsy cases of adult T-cell leukemia (ATL) complicated by a severe hypercalcemia are presented. In two of them, the hypercalcemia itself was the direct cause of death. There was no evidence of an increase of serum PTH in all three cases. Prostaglandins were within normal range in two of them. By a bioassay, a bone-resorbing factor, osteoclast activating factor (OAF)-like substance, was demonstrated in the culture medium of leukemic cells from one patient. Also, various degrees of osteoclastic activation were found in the bones of all three patients by the postmortem examination. It may be that the hypercalcemia occurring in cases of ATL is partly caused by the humoral factor, which is released from leukemic cells and activates a bone resorption by osteoclasts. Similar cases in which a significant activation of osteoclasts was practically demonstrated by histopathologic examination in addition to the detection of a bone-resorbing factor have been rarely reported.