The Use of Insulin Dynamics in the Evaluation of Streptozotocin Therapy of Malignant Insulinomas1

Streptozotocin, an antibiotic with diabetogenic and antitumor effects, was administered to two patients with malignant insulinomas and the effects on insulin secretion and glucose dynamics were evaluated. One patient, who had a dramatic alleviation of hypoglycemic episodes with normalization of fasting plasma glucose and insulin values, continued to have mild abnormalities in her responses to oral leucine. The second patient had an equivocal clinical response with some improvement in fasting plasma insulin and glucose levels, but no improvement in her response to tolbutamide. It is concluded that: (1) streptozotocin is the most effective agent currently available for the treatment of malignant insulinomas; (2) plasma glucose and insulin responses to glucose, tolbutamide, and leucine are useful in evaluating the therapeutic response to this agent; and (3) a treatment regimen can be designed for some patients which will result in tumor regression with minimal toxicity and minimal diabetogenic effects on normal islet cells.