It is widely acknowledged that prostate specific antigen (PSA) testing can lead to false-positives, overdiagnosis and overtreatment of prostate cancer. The current national clinical guidelines only recommend the test to a small group of patients and does not recommend neither systematic nor opportunistic screening for prostate cancer with the test.

The aim of this cluster randomized trial is to evaluate the effectiveness of a complex intervention aimed at improving the use of evidence based practice when using prostate specific antigen tests in general practice.

The complex intervention in this study is a so called cluster package which is meeting material to a quality cluster meeting as almost every general practitioner is a member of a quality cluster. Therefore, the investigators have developed a cluster package aimed at promoting an evidence-based use of the prostate specific antigen test to general practitioners.

Prostate cancer (PC) is the most common type of cancer among men in Denmark with an incidence of approximately 4.500 cases and 1.300 deaths every year. Usually prostate cancer develops very slowly and men with a detectable prostate tumor can live for many years without experiencing any symptoms. Autopsy studies of males who died of other causes finds PC in approximately 30 percent of males in their fifties and up to 70 percent of males in their seventies. From that perspective most men die with prostate cancer than because of it.

In Denmark the first examinations of a possible prostate cancer diagnosis take place in general practice. Every citizen in Denmark with a social security number has free and direct access to a general practitioner (GP) and works as a gatekeeper to the healthcare system. If the GP suspects prostate cancer in a patient the GP has the possibility to measure the level of prostate specific antigen (PSA) in a blood sample. If the level of PSA is high it may indicate the presence of prostate cancer.

However, according to the national clinical guidelines on detection and diagnostic investigation of prostate cancer the PSA-test is only recommended on a small patient group with very specific and rare symptoms. Furthermore they do not recommend neither systematic nor opportunistic screening with the PSA-test.

The reason for the rather restrictive guidelines for PSA-testing is to avoid overdiagnosis and overtreatment of prostate cancer. A high level of PSA in a blood sample is not necessarily due to prostate cancer but could also be elevated by other conditions such as cystitis or an enlarged benign prostate. Even if the further examinations at a urology department in a hospital finds prostate cancer in the patient it is potentially indolent cancer and not a clinically important tumor which is an prostate cancer overdiagnosis and could lead to unnecessary treatment which is overtreatment. The treatment of prostate cancer could cause harms such as impotence, incontinence and faecal incontinence.

Since 2018, GP's in Denmark has been encouraged to cluster in groups of other GP's from their local area to work with quality development and form so called quality clusters. The aim of these quality clusters was to create a medical professional forum where the GP's could meet 2-4 times a year and exchange experiences with each other in a specific clinically relevant area decided by the cluster itself. One of the main points of the quality cluster concept was that the quality development work should be based on descriptive data from their own GP clinics. At present 116 quality clusters exist in Denmark and includes 3.519 GP's in 1.542 GP clinics.

By the same time of the establishment of the quality cluster a national organization called KiAP (a Danish acronym for Quality in General Practice) was founded. The primary purpose was to support the quality clusters with their quality development work. One of the supportive initiatives by KiAP is the development of cluster packages which is meeting material for the quality clusters on their cluster meetings. A cluster packages has one specific clinically relevant theme and consists of data, expert videos, reflection questions among other things.

The investigators have chosen to develop a cluster package about PSA-tests in general practice with the purpose to promote an evidence-based practice. A pilot study will be conducted in the development process. The aim of the study is to evaluate the effectiveness of the cluster package. Since the study is a cluster randomized trial the investigators invited all the Danish quality clusters to agree to use the cluster package on one of their cluster meetings. The participating quality clusters are randomized to an intervention group and a control group.

Inclusion Criteria:

• Quality clusters with a cluster coordinator
• Quality clusters willing to participate in a cluster meeting with PSA as a theme in 2025.

Exclusion Criteria:

• Quality clusters who already planned their cluster meetings in 2025.
• Quality clusters unwilling to await allocation before planning their cluster meetings in 2025.
• Quality clusters participating in the pilot study

Due to the nature of the intervention, it will not be possible to blind the GP's or members of the research team after the allocation. The primary outcome is blinded to the statistician and data manager is blinded until outcomes are analyzed