Failure of Thymectomy to Alter the Subsequent Course of Human Acute Leukemia in Drug-induced Remission.

I N RECENT YEARS there has been increasing evidence that the thymus may be the “master gland” concerned with lymphopoiesis nd immunit .1 In the mouse the thymus has been demonstrated to have a significant role in the pathogenesis of leukemia. Several different approaches have emphasized its importance. Thymectomy, in high leukemic strain mice, considerably reduces the incidence of spontaneous leukemia.24 The incidence of leukemia in hybrid mice bearing a thymic transplant from a high leukemic strain is considerably increased.5 Radiation-induced lymphoid tumors in low leukemia strain C57 mice are significantly reduced if the mice are thymectomized before irradiation or as late as 12 weeks after irradiation.6-7 Lymphomas develop with moderate and reproducible frequency in thymectomized irradiated mice bearing grafts of normal isologous thymus.5 The incidence of carcinogeninduced leukemia in strain DBA mice is reduced by thymectomy while autoplastic grafting of the thymus to thymectomized mice raises the incidence to prethymectomy level.9 Inoculation of passage virus “Gross” agent A induces leukemia in the low leukemia strain C3H mice; however, the incidence of leukemia is remarkably reduced when the mice are thymectomized.’#{176}” Similarly, thymectomy in the high leukemic AKR strain, performed at the age of 3 to 4 weeks of life, prevents the induction of premature leukemia by Cross agent A inoculation.12 Very little information is available as to whether the thymus has a comparable role in human leukemogenesis. Dean et al., in 1951,1314 reported that thymectomy in previously untreated children with acute and subacute lymphocytic leukemia failed to induce remission. Soutter and Emerson’5 performed elective thymectomy in a 57-year-old man with aregenerative anemia associated with monocytic leukemia. The patient died 8 months postthymectomy, and the postmortem hone marrow findings were said to be typical of monocytic leukemia. With these observations in mind, we decided to conduct a limited pilot study on the effect of thymectomy on the course of human leukemia. It is obvious that one must be cautious in applying the results of animal studies directly to human disease. However, it appeared that extirpation of the thymus during the period of drug-induced remission might simulate to some degree the experimental model in mice. To the best of our knowledge, no similar attempt under these conditions has been made previously. After the induction of complete clinical and hematologic remission by accepted chemotherapeutic means, thymectomy was performed in 3 patients