Serum lactic dehydrogenase activity after excision of transplanted tumors.

In previous communications (4, 5) we have reported that in animals with carcinoma, whether induced, transplanted, or spontaneous, there was an increase in serum lactic dehydrogenase (LDH) activity. A direct relationship was also demonstrated between LDH activity and tumor growth and regression. As the tumor grew, the LDH activity was progressively elevated, and, as the tumor regressed, LDH activity decreased. An interesting problem arising from these studies is the effect of removing transplanted tumors at different stages of growth on the serum LDH pattern. Does the removal of tumor cause a sudden return of serum LDH to its normal level, or does the LDH activity gradually decline to its normal level? Another question is whether or not the tissue LDH level varies with the rise and fall in serum LDH. The present report summarizes the results of experiments designed to answer these questions.