Objective: to observe the influence of aging on urinary secretion of 3-hydroxyproline (3-Hyp) in normal subjects and in cancer patients and study the effects of aging on the accuracy of urinary 3-Hyp as a general-purpose cancer screening test.
Design: We reanalyzed, from the aspect of gerontology, the amounts of 3-Hyp in the urine samples of the 211 healthy persons and 94 patients with cancer reported earlier. The two groups were divided in 3 age subgroups: adult, 30 to 44 years, middle-aged, 45 to 64 years, and aged, 65 years and older. The cancer stage was separated into 3 categories: stage 1, the early stage without any invasion, stage 2, locally invasive with no distant metastasis, and stage 3, advanced cancer. The correlation of age and urinary 3-Hyp was analyzed in normal subjects and cancer patients. Sensitivity and specificity were calculated for different cutoff points in the diverse groups to construct the receiver operating characteristic (ROC) curves.
Main Results: We observed that aging decreases the urinary secretion of 3-Hyp in normal subjects, with a correlation coefficient of -0.250 (p<0.001). The mean levels of urinary 3-Hyp in patients with cancer were significantly higher than in the normal subjects, p=0.005. The correlation coefficient of urinary 3-Hyp and age was not significant (0.100) in cancer patients. The cutoff points of 0.800mg/g creatinine of urinary 3-Hyp for persons under 65 years of age and 0.600mg/g creatinine for persons 65 years or older were the best thresholds for cancer screening. In the ROC analyses, we observed that 3-Hyp has higher accuracy for cancer screening in the aged group for all stages together and in the aged and middle-aged for early stages of cancer.
Conclusions: The urinary 3-Hyp test was more effective for cancer screening in old persons (65 years or older), where cancer is more frequent and more difficult to discover. The authors stress the necessity and importance of verifying the effectiveness of urinary 3-Hyp for general cancer screening in a larger population and in a community set.