Background?The World Health Organization emphasizes cancer screening to reduce cancer mortality. Health examinations represent the most prevalent opportunity for cancer screening in China, warranting attention to the status of missed cancer detection during these examinations.
 
Objectives?To estimate the missed detection rate of early-stage common cancers in health examinations in China ? and to provide evidence for improving the health benefits of cancer screening through physical examinations. 
 
Methods?Based on public data such as health examination coverage and population-based early-stage cancer proportion ? a model was constructed to simulate the missed detection process. Using Bayesian test theory ?the theoretical early-stage detection rate was calculated with health examination rate and expected early detection proportion as prior probabilities ? and the actual early-stage proportion as posterior probability to estimate the early missed detection rate. The equivalent early detection proportion was further derived. 
 
Results?When the health examination rate was 30% and the expected early detection proportion was 90% ? the aggregate missed detection rate of five common cancers was 47.9% ? among them ? female breast cancer had the lowest missed detection rate (15.4%) ? esophageal cancer the highest (57.4%) ? followed by gastric cancer (49.2%) ? colorectal cancer(55.7%) ? and lung cancer (56.4%). When the health examination rate increased to 40% (with the expected early detection proportion maintained at 90%) ? the aggregate missed detection rate rose to 59.2% ? when the health ex-amination rate decreased to 20% ? the aggregate missed detection rate was 27.7%. Under different expected early detection proportions ? the missed detection rate showed a regular change ? at a health examination rate of 30% ?the aggregate missed detection rate was 42.2% corresponding to an expected early detection proportion of 80% ?and 35.1% corresponding to 70%. According to the current health examination coverage (30.52%) ? the aggregate equivalent early detection proportion of the five common cancers was 41.3% ? among which female breast cancer(74.3% ) was significantly higher than other cancer types ? while esophageal cancer (31.7% ) and lung cancer (32.7%) were the lowest. 
 
Conclusion?Nearly half of the detectable early-stage cancer patients are missed in health examinations? and the insufficient effectiveness of early detection in health examinations is the core problem. Without improving the detection effectiveness? simply increasing the health examination rate will increase the number of early missed detections. Optimizing the quality of health examinations should be the priority to reducing the missed detection rate.

Missed detection rates under the conditions of health examination rates and expected early detection ratios and missed detection rates for different cancer types