Correlated Expression of Glutathione S‐Transferase‐π and c‐Jun or Other Oncogene Products in Human Squamous Cell Carcinomas of the Head and Neck: Relevance to Relapse after Radiation Therapy

Abstract

The expression of glutathione S‐transferase (GST)‐π and four oncogene products, c‐Jun, c‐Fos, c‐H‐Ras, and c‐Myc, in human squamons cell carcinomas of the head and neck was investigated immunohistochemically before and after radiation therapy, to examine whether these oncogene products might be involved in GST‐π expression, and also to examine the relationship between their expression and therapeutic response. Clinical response to radiation was evaluated in terms of both tumor regression and relapse over two‐year follow‐up periods. The overall positive rates in 83 carcinoma specimens before therapy were 60.2% for GST‐π and 28.9–51.8% for the individual oncogene products, the positive rates for the oncogene products being higher in GST‐π‐positive than in GST‐π‐negative cancers. c‐Jun was most highly correlated with GST‐π expression. Following radiation, the expression of GST‐π and the oncogene products was altered in about a half of 30 patients. Eleven of the 18 patients who exhibited prior positivity for GST‐π showed negative conversion, while 4 of the 12 patients with prior negativity demonstrated positive conversion. In most cases, changes in c‐Jun staining coincided with those in GST‐π. Regarding clinical response to radiation therapy, the positive rates for GST‐π and c‐Jun before radiation were higher in the residual cancer or relapse cases than in the group showing complete response without relapse. Examination of 26 patients with laryngeal cancer revealed that relapse occurred more frequently in cases exhibiting positive reactions for GST‐π,c‐Jun, or c‐H‐Ras. These results suggest a direct link between c‐Jun and GST‐π in head and neck cancers before and after radiation. Although GST‐π and the oncogene products can be influenced by radiation, GST‐π and c‐H‐Ras expression may be a risk factor for relapse of laryngeal cancer.