The overexpression of
cyclic AMP (
cAMP)-dependent protein kinase (PKA) has been reported in patients with
cancer, and PKA inhibitors have been tested in clinical trials as a novel
cancer therapy. The present study was designed to characterize the population distribution of extracellular activity of
cAMP-dependent protein kinase (ECPKA) and its potential value as a
biomarker for
cancer detection and monitoring of
cancer therapy. The population distribution of ECPKA activity was determined in serum samples from a Chinese population consisting of a total of 603 subjects (374 normal healthy volunteers and 229
cancer patients). The serum ECPKA was determined by a validated sensitive radioassay, and its diagnostic values (including positive and negative predictive values) were analyzed. The majority of normal subjects (>70%) have undetectable or very low levels of serum ECPKA. In contrast, the majority of
cancer patients (>85%) have high levels of ECPKA. The mean ECPKA activity in the sera of
cancer patients was 10.98 units/mL, 5-fold higher than that of the healthy controls (2.15 units/mL; P < 0.001). In both normal subjects and
cancer patients, gender and age had no significant influence on the serum ECPKA. Among factors considered, logistic analysis revealed that the disease (
cancer) is the only factor contributing to the elevation of ECPKA activity in
cancer patients. In conclusion, ECPKA may function as a
cancer marker for various human
cancers and can be used in
cancer detection and for monitoring response to
therapy with other screening or diagnostic techniques.