Twenty patients with malignant
carcinoid tumors were treated for 6 months with recombinant
interferon alfa-2b (IFN alpha-2b; Intron-A; Schering Corp., Bloomfield, NJ) at a mean dose of 5.9 megaunits three times per week. Eleven of the 20 patients (55%) had a greater than 50% reduction of
tumor markers (urinary 5-
hydroxyindoleacetic acid or plasma
neuropeptide K), showing objective
tumor response. Six patients (30%) had stable disease with no significant change in
tumor markers or
tumor size, and three (15%) had progressive disease with an increase in
tumor markers and size. These results are similar to those reported earlier for treatment with natural leukocyte IFN in patients with
carcinoid tumors. Only two patients (35%) had a slight reduction of
tumor size after 6 months of treatment. Three patients developed
neutralizing antibodies to IFN alpha-2b. Two of these patients initially showed an objective response, which lasted until IFN
antibodies developed. In one of these patients, a change to human leukocyte IFN resulted in normalization of antibody titers within 3 months, and the patient had a second objective clinical response. There was no correlation between development of IFN
antibodies and development of autoimmune phenomena such as increased titers of
antinuclear antibodies or thyroid
autoantibodies. IFN alpha-2b seems to be as potent as human leukocyte IFN in the treatment of patients with malignant
carcinoid tumors, but it is important to recognize that
antibodies neutralizing IFN may develop in some patients, with concomitant loss of antitumor effects. A change to natural leukocyte IFN might be beneficial in these patients.