In her study, Le Clercq examined patients who were diagnosed with colon cancer between 2001 and 2010 in South Limburg (Maastricht, Heerlen and Sittard). Of these patients, 3% had undergone a colonoscopy less than five years ago without any signs of cancer. This is known as post-colonoscopy colon cancer. Interestingly, this figure is much higher in North America, namely, 9%. This is because the Netherlands has specialised gastroenterologists who carry out the study and are subject to strict quality requirements. 'Of course there's always room for improvement when it comes to the quality of the research,' says Le Clercq. 'Technical factors were involved in the majority of these post-colonoscopy cancer diagnoses. Awareness and better training for endoscopy technicians can lower this 3% figure even more and even help prevent post-colonoscopy cancer entirely. We deliberately chose South Limburg because this region has the lowest migration rate, meaning the survey population remains more or less the same.'

In another study carried out as part of her dissertation, Le Clercq investigated the nomenclature of interval colon cancer and post-colonoscopy cancer. The recommendations in her study were immediately applied in the Dutch medical field and adopted by the RIVM in the national screening for colon cancer.

Colon cancer is one of the most common forms of cancer, which is caused by polyps that slowly develop into cancerous tumours. In principle, colon cancer can be prevented if a polyp is discovered and removed in time. Each year, 15,000 people are diagnosed with colon cancer and 5,000 people die as a result of this disease. The national screening for colon cancer was introduced in 2014 to detect colon cancer and polyps at an early stage and to reduce mortality rates.