Radiation-associated changes in tissues and tumours

Abstract

With increasing use of radiation therapy in cancer treatment and longer survival of patients, assessment of radiation-associated changes in tissues and tumours has become an important issue in modern pathology. Radiation induces injuries mainly through DNA damages which may affect apoptotic pathways, acute and chronic ischaemia, and subsequent tissue repair and fibrosis. Irradiated native cells are characterized by both nuclear and cytoplasmic enlargement, associated with degenerative changes. Distinction from true neoplasia relies on low proliferative activity, relatively low nuclear–cytoplasmic ratio, and fine but vacuolated nuclear chromatin. Some pseudomalignant radiation-associated changes in various organs, such as radionecrosis in brain, colitis cystica profunda in colon, atypical basal cell hyperplasia in prostate, atypical vascular lesions in skin and pseudocarcinomatous proliferations in urinary bladder, should also be recognized to avoid a misdiagnosis of malignancy. Rarely, due to genetic instability and accumulation of mutations, malignancies can arise within the field of radiotherapy, years after completion of treatment. These neoplasms include carcinomas, sarcomas (e.g. malignant fibrous histiocytoma, osteosarcoma and angiosarcoma) and leukaemia/lymphoma. They often present late and are associated with aggressive clinical behaviour and poor treatment response. Earlier and accurate pathological diagnosis, with awareness of potential diagnostic pitfalls, is thus prudent in guiding subsequent management of this group of malignancies.