After radiotherapy testosterone stimulation is unable to increase growth in the Dunning R3327-PAP prostate tumour

A study was carried out to investigate whether testosterone treatment is ab le to influence tumour growth in a rat prostatic adenocarcinoma previously treated with castration and high-dose fractionated irradiation. Copenhagen x Fisher rats bearing the androgen-sensitive, well-differentiated Dunning R 3327-PAP tumour were castrated and thereafter treated with external beam ra diation with photons from a 4-MV linear accelerator. One month after irradi ation, substitution with subcutaneous testosterone was started. Tumour volu mes and rat weights were monitored up to 256 days after castration, and at the end of the study a microscopic analysis of the tumours was performed. I rradiation delayed tumour growth as compared with untreated tumours. Castra tion delayed tumour growth, but a hormone-refractory relapse to doubled tum our volume was seen within 45 days. If testosterone was added after castrat ion, the tumours grew rapidly. However, testosterone failed to increase tum our growth when given to rats treated with orchiectomy and irradiation. His tological examination showed that the irradiated tumours still contained tu mour epithelial cells, but these cells apparently do not respond to testost erone stimulation. The well-differentiated and androgen-sensitive rat prost atic adenocarcinoma did not grow after irradiation despite stimulation with testosterone. This indicates that the malignant cells lose their androgen sensitivity after high-dose irradiation.