The benefit of B.C.G. in prolonging chemotherapy-maintained complete remissions in adult acute leukæmia was studied. Twenty consecutive patients received intermittent chemoimmunotherapy with cytarabine, vincristine, prednisone (O.A.P.), and liquid Pasteur B.C.G. administered by scarification. The durations of remission were compared with those of a similar group of thirty-three consecutive patients maintained on O.A.P. chemotherapy alone. Eleven of the twenty (55%) O.A.P.+ B.C.G. treated patients remain in remission with an estimated median duration of 91 weeks. Only 14 of 33 patients (42%) maintained on O.A.P. remain in remission with a median duration of 50 weeks (P= 0·03). Immunotherapy was significant only for patients with acute myeloblastic leukæmia (A.M.L.) and not for lymphoblastic or undifferentiated leukæmia. Thus, ten of fourteen A.M.L. patients maintained on O.A.P.+B.C.G. are in remission (median duration 72 + weeks) compared with nine of twenty-one O.A.P.-maintained patients (median duration 60 weeks) (P=0·04). General immunocompetence was augmented by B.C.G. The best prognostic immunological test was the patients' in-vitro lymphocyte blastogenic reactivity to autologous remission bone-marrow cells: all five patients who reacted vigorously have relapsed compared with none of the six who failed to react or reacted weakly.
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