Radiation injury of the normal and neoplastic prostate.

Tissue samples from 40 patients with prostatic adenocarcinoma treated by radiation therapy were evaluated simultaneously by three observers to establish criteria for distinguishing residual tumor from radiation-induced atypia. Sections from 10 patients irradiated for nonprostatic pelvic neoplasms served as controls in addition to pretreatment biopsies from the determinate group. Patients had been treated by external x-irradiation, the majority receiving 6200-7400 rad to the prostate and pelvis over 7 to 8 weeks. Positive (tumor) biopsy incidence in the determinate group was 80% at 18 months, 40% at 36 months, and 43% in later samples. The following features were characteristic of radiation injury in the prostate: decreased ratio of the number of tumor glands to stroma, atrophy and squamous-like metaplasia of non-neoplastic glands with or without atypia, stromal fibrosis, arterial lumenal narrowing due to myointimal proliferation, foam cells within vessel walls, and fibrosis and atrophy of seminal vesicles. Criteria not useful for diagnosing radiation injury included architectural pattern or differentiation of tumor, cytologic features of tumor cells, inflammatory infiltrate, and ratio of normal glands to stroma. Ionizing radiation produced characteristic lesions in neoplastic and non-neoplastic prostatic glands, stroma, and blood vessels, and the sum of these changes was a reliable indicator of prior radiotherapy. An understanding of the morphologic effects of radiation injury of the prostate allowed distinction between residual prostatic adenocarcinoma and radiation-induced atypia of non-neoplastic glands.