Transforming growth factor beta: a promotor of late connective tissue injury following radiotherapy?

Transforming growth factor beta (TGF-beta) is a peptide which has a fundamental role in controlling proliferation of many cell types. Its main effect upon connective tissues in vivo is to stimulate growth. It can result in endothelial cell proliferation but tends to inhibit epithelial cell growth. Damage to the connective tissues and the vasculature are the principal findings in late radiotherapy damage. Following the initial cellular depletion after radiotherapy, an abnormal proliferation of these tissues occurs, which does not respond to normal feedback mechanisms. Immunocytochemical staining for TGF-beta has been performed upon six patients who had received pre-operative radiotherapy and three patients who had surgery alone for large bowel tumours. Transforming growth factor beta was found in relation to the pathological changes of late radiation damage in the non-tumour-bearing tissues of four out of six previously irradiated patients, but in none of the non-irradiated patients. This paper proposes that TGF-beta activity may modulate late post-radiation changes.