The Quebec Tumor Registry is a central data collection system designed to record all new cases of malignant tumors—also known as "cancer"—that occur in Quebec, with the aim of ensuring continuous monitoring of the population's health status. Cases are identified based on hospitalizations in general and specialized care hospitals in Quebec, mortality data, and record exchanges with neighboring provinces. This results in a problem regarding the completeness of case reporting and the accuracy of the actual time of diagnosis. Indeed, thanks to the diagnostic techniques and minimally invasive surgical procedures used today, certain tumors located in easily accessible sites can be diagnosed and treated on an outpatient basis or in a doctor’s office without requiring hospitalization or same-day surgery. These cases are therefore not recorded in the Quebec Tumor Registry or are recorded at a more advanced stage of the disease, which then requires hospital care. Several cancers—particularly prostate and bladder cancers, as well as melanomas—are thus excluded from the Quebec Tumor Registry for this reason. Studies are underway to address this gap by using complementary data sources to feed the Quebec Tumor Registry, particularly laboratory reports, data from radiation oncology centers, and procedures billed by physicians. (R.A.)