“More and more people are living with cancer. It is expected that the number of people living with cancer will rise from 118.000 in 2019 to 156.000 in 2032. They are often confronted with symptoms and long-term consequences of the cancer and its treatments and this can have major impact on the society. We will have to pay attention to those consequences, including research into possible long-term effects; one of the aims of my thesis.”


The number of patients newly diagnosed with colorectal cancer is increasing. Due to early detection and innovations in colorectal cancer treatment, the survival of patients diagnosed with colorectal cancer has been improved over the last years. As a result, more patients are confronted with the late effects of cancer treatment which can manifest many years after completion of the treatment. The general practitioner is the gatekeeper in the Dutch healthcare system and involved in different stages of the disease: from prevention to end-of-life care. At the moment, there is limited insight into the utilisation of primary care among colorectal cancer patients. These insights are essential in order to detect potentials for early detection of cancer and will provide knowledge on the late effects of cancer for which patients consulted their general practitioner. Furthermore, having information on the use of certain drugs among cancer patients will inform on potential associations between drug use and the occurrence of cancer. This thesis aimed to get more insight into the utilisation of primary care among colorectal cancer patients, including their healthcare seeking behaviour before diagnosis, the effect of its pharmacological treatment on the occurrence of heart failure, and associations between drug use and the risk of colorectal cancer.


To be able to conduct these population-based observational studies, a new cohort was created by linking the General Practitioner (GP) Database of the PHARMO Database Network to the Netherlands Cancer Registry (NCR). This resulted in the PHARMO GP – NCR cohort which contains information on the cancer itself (from the NCR) and primary care utilization before and after diagnosis (from the GP Database) of more than 135,000 cancer patients in the period 1998-2014.  Several studies were performed using data from this linked cohort including:

What’s next?

This thesis only describes a few examples of studies using data from the PHARMO GP – NCR cohort, but many other (pharmaco)epidemiological studies are possible, such as investigating the prevalence of certain comorbidities among patients with cancer and assessing the association with the development of cancer. Besides studying the effect of levothyroxine and PPIs on the risk of colorectal cancer, the PHARMO GP – NCR cohort can be used to study the safety of several (other) drugs as well. Colorectal cancer was used as example in this thesis given the high incidence in the Netherlands and the increasing number of survivors, but the NCR collects information on all types of cancers.

“Combined data on primary cancer and cancer has shown to be a valuable source for performing (pharmaco)epidemiological studies in the primary care setting. I encourage other researchers to make use of this valuable source of data and further improve patient care.”

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