Hydroxyproline excretion in patients with breast cancer and response to treatment.

The urinary excretion of hydroxyproline, measured as the hydroxyproline: creatinine ratio, was useful in monitoring the progression of metastatic cancer of the breast. After new treatment was started changes in the hydroxyproline excretion occurred earlier than other clinically observable responses. The test could therefore be used for predicting the response to treatment and early detection of the sensitivity of the tumour to hormone therapy.