Identical-twin (syngeneic) marrow transplantation for hematologic cancers.

The Seattle Marrow Transplant Team treated about 130 patients (age 4-68 yr) for hematologic cancer with supralethal chemoradiotherapy and bone marrow transplantation (BMT) from the normal genetically identical twin. The procedure was well tolerated. The principal problem was tumor resistance. Nevertheless, BMT for acute leukemia in relapse still cured about 20% of the patients. Moreover, BMT performed while in complete remission cured about 50% of patients with acute lymphocytic leukemia or acute nonlymphocytic leukemia. Sixteen patients received transplantation in the chronic phase of Ph1+ chronic granulocytic leukemia (CGL). All showed disappearance of all Ph1+ cells. Two died of pneumonitis. Of the 14 who are alive, 3 continue to have CGL 37-76 months after BMT and 11 remain in complete hematologic and cytogenetic remission without any Ph1+ metaphases at 31-108 months (median = 68) after BMT. Thus the Ph1-positive clone can be ablated and blast crisis prevented. BMT in the accelerated or blastic phase was far less effective. Syngeneic BMT also benefited or cured patients with lymphoma, hairy-cell leukemia, and multiple myeloma. Therefore, BMT should be considered for every patient who has a hematologic cancer and an identical twin.