This is a multi-centre, prospective cohort study, aiming to evaluate a blood test in early detection of the four common cancers, based on the investigation of the circulating tumour DNA (ctDNA).

Primary objective: To evaluate the performance characteristics of the blood ctDNA test in early detecting cancers.

Secondary objectives:

• To evaluate the performance characteristics of the test in determining the origin of tumour, as compared to the findings of the imaging diagnostic tests.
• To determine the risk of cancers development in the high-risk population, as compared to that in the moderate-risk group.

This is a multi-centre, prospective cohort study recruiting participants aged 40 or above, who present at the Outpatient Clinic of the study hospitals either for periodically follow-up visits for their chronic conditions, or for annually health check-up. The study will be conducted at the Medical Genetic Institute, in collaboration with the University of Medicine and Pharmacy at Ho Chi Minh City, Vietnam and other collaborating hospitals.

The potential participants, who satisfy all inclusion/exclusion criteria will be recruited into this study. These potential participants should not have history of cancer before being enrolled in the study.

At enrolment, each participant will answer to a pre-designed questionnaire to provide demographic information, past major medical history and clinical warning signs of cancers, and then provide 10mL of blood for analysing the circulating tumour DNA (ctDNA).

Each participant will get either ctDNA detected or ctDNA not detected.

For those having ctDNA detected in their blood, they will then undergo the screening and diagnostic tests for cancers based on the prediction of tumour origin provided in the test findings report. If the cancers lab-confirmed, patients will then be followed up and managed for their disease according to the guidelines of the Vietnam Ministry of Health and/or the international guidelines on cancers. At 12 months (+/- 1 week) following the enrolment, these patients will be contacted to collect information about their health, in general and their cancer status, in particular.

For those having ctDNA detected in their blood but the present of a mass inside participants' body could not be detected using the imaging diagnostic tests; and for those, who don't have ctDNA presenting in blood, phone calls will be made at 6 months (+/- 1 week) and 12 months (+/- 1 week) following the enrolment to collect information related to participants' health status as well as cancer progress (if possible).

The enrolment is anticipated to last for approximately 6 months.

Inclusion Criteria:

• Aged 40 or above at enrolment
• Neither clinical suspicion of cancer nor history of confirmed cancer has been reported
• Agree to be contacted at 6 months and 12 months following enrolment to collect information about general health status and progress of cancer (if possible)
• Provide written informed consent

Exclusion Criteria: If a potential participant has any one of the following criteria, he/she will not be able to be enrolled in the study:

• History of cancer (cancer has either been confirmed or been treated within the past 3 years)
• History of blood transfusion or bone marrow transplantation within the past 3 years
• Does not agree to participate in study
• The subject has clinical manifestations of pregnant.

The study population will include both males and females, aged 40 or above, who have no history of cancer. These people present at the Outpatient Clinic of the study hospitals either for periodically follow-up visits for their chronic conditions or for health check-up.The eligible participants will have to satisfy all of the inclusion and exclusion criteria to be recruited into this study.

Anonymised data of this study may be requested for publication by journals. Sharing anonymised data with future similar/suitable studies will be decided by the sponsor, PIs and the authority agency where the data was collected. No identifiable information will be shared with any other person/organisation than authorized in the study.