Systemic treatment of advanced prostatic cancer: development of a new system for defining response.

The low incidence of measurable or evaluable metastases in patients with prostatic cancer makes evaluation of response difficult. This is particularly true in patients with bone metastases only. With a digital model it is possible to measure quantitatively from the radioisotope bone scan the total area of skeletal involvement by metastatic tumor. Definitions of response in bone have been derived from this model. These response criteria have been compared to response in acid phosphatase determinations and clinical status in a study of 44 patients with advanced prostatic cancer treated with estramustine phosphate. Based on serial quantitative bone scans, serial measurements of acid phosphatase levels and repeat clinical evaluations a system is proposed for defining response to systemic therapy that is applicable to the majority of patients with metastatic prostatic cancer.