Effects of interferon on tumor tissue content in liver metastases of human carcinoid tumors.

In 21 patients ultrasound-guided cutting biopsies, from carcinoid metastases of the liver, were taken before and after therapy with alpha-interferon. Each biopsy was examined under light microscopy and the amount of tumor tissue and connective tissue was quantified and then correlated to objective response to interferon therapy. A significant reduction of the amount of tumor tissue, in spite of unaltered metastatic size and a corresponding increase in connective tissue, was seen after interferon therapy. A more pronounced reduction of tumor tissue occurred after long-term interferon therapy. A positive correlation between objective therapy response and tumor tissue reduction was also present. Patients responding poorly, or not at all, to therapy did not show any significant decrease in tumor tissue. Since treatment with immune response modifiers is expected to increase in the near future, it is important to choose the right investigations for therapy monitoring, and since all patients in this investigation had unchanged tumor size on repeated radiological examinations, it is obvious that microscopic examination of core biopsies is a better method for evaluating effects of long-term therapy than tumor size measurement with radiological techniques. Further, the results may indicate that interferon exerts a cytotoxic effect on carcinoid tumor cells in vivo.