The development of a national surveillance system, the Multi-Source Cancer Surveillance System (SMSC), to complement the registry-based system was recommended by the commission evaluating the health consequences of the Chernobyl accident. The system is based on the cross-referencing of anonymized data from three sources (PMSI, ALD, and ACP reports). The objective of the pilot study was to assess the relevance and feasibility of implementing the SMSC. The study focused on thyroid cancer in two regions: Île-de-France and Nord-Pas-de-Calais. Data collection from the ACP reports was conducted retrospectively (2004) using a computerized form. 423 ACP data sheets for thyroid cancer were submitted by volunteer ACPs from the two regions. These were cross-referenced with data from ALD cancer records (1,159) and the PMSI (2,947) for the year 2004. The matching rate (number of ACP cases found in the other sources) observed was 84% (three sources), 81% (ACP, PMSI), and 48% (ACP, ALD cancer). The implementation of the system revealed that the chosen IT solution was complex for nationwide deployment. This complexity stems from the technical difficulties encountered during the project. At the conclusion of the pilot, two areas for developing the SMSC at the national level were identified: - in the immediate term, cross-referencing the PMSI and ALD cancer sources for descriptive purposes and to generate surveillance indicators; - in the medium term and in parallel with the first area, studying the conditions for establishing the national ACP database. (R.A.)