Enhancement of radiation effects by alpha interferon in the treatment of small cell carcinoma of the lung.

The effects on lung tissue and tumor of natural human alpha interferon (IFN) and radiotherapy were investigated in a multimodality treatment program for selected patients with small cell carcinoma of the lung (SCLC). Interferon was given first as a single agent, then concomitantly with radiotherapy to 12 previously untreated patients with limited disease. At disease progression outside the chest, interferon was discontinued and combination chemotherapy was initiated. In the first series, 7 patients received a high interferon induction dose (800 X 10(6) IU i.v. over 5 days) followed by low-dose maintenance therapy (6 X 10(6) IU i.m. TIW), median total dose 1380 X 10(6) IU (range 794-2074). At local progression, split-course radiotherapy, 55 Gy/20 F/7 wk, was added to interferon therapy. In the second series, 5 patients received low-dose interferon from the start (6 X 10(6) IU i.m. daily) combined with twice-a-day fractionated radiotherapy 44 Gy/40 F/4 wk. Median total dose of interferon in this series was 698 X 10(6) IU (range 354-828). Tumor response and normal tissue reactions were evaluated by monthly chest X rays, 3-monthly CT scans, restaging bronchoscopies and by serial respiratory function tests. Autopsy specimens from both lungs within and outside the radiation field were systematically evaluated when available. After the completion of radiotherapy, there were 4/7 CR in the high-dose IFN group compared to 3/5 CR in the low-dose IFN group. Rapid shrinkage of huge tumor masses was observed. At 2 months post radiotherapy radiological grade III fibrosis occurred in 4/7 patients in the high-dose and 1/5 patients in the low-dose group. Lung function studies showed a significant decrease in diffusing capacity and in lung volumes. Seven patients died within 12 months from start of interferon treatment, one of them from treatment complication. At autopsy the tumor area was in most cases replaced by severe fibrosis. Outside the radiation field lung fibrosis was mild. Our results suggest enhancement of radiation effect by interferon with a possible dose and/or schedule dependence of interferon and radiotherapy and call for more clinical studies of IFN and radiotherapy in combination.