EARLY STAGE CANCER SCREENING THROUGH TUMOR MARKERS IN BLOOD TESTS

26/11/2018
Article on “Tuổi Trẻ cuối tuần” newspaper on 18/11/2018
Writer: Dr.Nguyễn Vĩnh Tường, Medical Manager of Victoria Healthcare .
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Cancer screening to detect early stage of cancer is the goal of contemporary medicine, but there is no practical method for it, up until now. However, in general, the following methods could be considered as general cancer screening: 

✅Blood tests: If you have cancer, a particular protein will be created by the cancer cells themselves, so called tumor marker. Figuring out based on these particular proteins by blood test, you will know the type of cancer, such as liver cancer creates protein AFP, colon cancer creates CEA, pancreas cancer creates CA19-9, lung cancer creates CYFRA 21, ovarian cancer creates protein CA 125 ...

✅Doing blood test to detect gene causing cancer: This is the latest cancer detection method because cancer is the result of a gene mutation. For example, by doing a blood test, BRCA2 gene has been discovered as the cause of breast cancer, the same as APC gene which causes colon cancer...

✅Image analysis: CT scan, full body MRI,  and PET CT are image analysis methods based on the reaction of up taking high glucose of cancer cell to metabolize. They inject to testers a quick absorbing glucose attaching position; as absorbing radioactive material in the body, the testers then release gamma rays. At this time, the PET/CT will calculate data from these gamma rays to collect images from different cells of the body. As a result, cells’ abnormalities in the metabolism will be detected, just before a structural change.

✅Cancer screening tests on target organs: Do esophagogastroduodenoscopy-EGD and colonoscopy to screen stomach cancer and colon cancer; do breast ultrasound, mammography and MRI for screening breast cancer; Do PAP’s Smear to screen cervical cancer...

Many patients wonder about the necessary of cancer screening in detecting different types of cancers by using all these methods. Health facilities usually chose blood test because blood test is easy to do in detect tumor markers (CEA, CA19-9, CA 125, CYFRA 21-1, AFP, PSA…are common to tumor markers tests); it is also cheaper than other tests; and it does not take so much time to be done.
🔰TUMOR MARKERS

According to American Society of Clinical Oncology-ASCO, tumor markers are substances that are created by cancer cells as well as normal cells in the body in response to cancer or normal condition. However, they are created at much higher level in cancerous conditions.

Many different tumor markers are associated with one kind of cancer or more different cancer types, but there is no 1 tumor marker presenting to all kind of cancers. This means there is no blood test that can show existence of cancer or not.

There are some limitations in using tumor markers for screening cancers because there are many noncancerous condition with high level of tumor markers such as CEA will increase level in case of enteritis or smoking a lot. AFP will increase level in case of hepatitis. PSA will increase its level in case of prostatitis. 

Therefore, not all patients with high tumor markers have cancer. In contrast, tumor markers may be at normal level in cases of cancer or even late stage of cancer. AFP may be negative in 40% of early stage of liver cancers, CEA is also negative for more than 60% of colon cancer. CA125 in ovarian cancer case is much more complicated because ovarian cancer will 50% increase and 50% will not increase level of CA 125, and many cases are common in women who have CA 125 increased such as endometriosis, pelvic inflammatory disease, and smoking.
In short, do tumor marker tests without doctor’s consultation may make patients confused and worried of getting cancer and may also cost them much money and time to figure out the cancer to treat but find nothing, or make patient confident enough not to take further cancer screening tests .

ASCO advices that tumor markers only work as supplement information for a suspected cancer disease. For example, ovary should be examined by doing vaginal ultrasound, contrast-enhanced pelvic CT scan, and measuring CA 125 to evaluate the  potential risk of cancer and doctors will decide whether to follow up or have surgery; or use to monitor patients who go through cancer treatment, to screen for recurrence of cancer, if this cancer is found to increase its tumor marker. For example, colon cancer usually increases with CEA, so doctors usually order CEA measurement during follow-up of patients with colon cancer; or measure AFP in case of liver cancer. If AFP increases prior to treatment, during follow-up if AFP level increases, the cancer may recur; so, be careful.

None of associations of cancer, as well as gastroenterology, gynecology, and respiratory recommended healthy people to do cancer screening by measuring tumor markers periodically as much as possible because the results will be varied, this makes it difficult to doctors to explain to the patient.

It can be said that no method is the best, each one has its own feature and limitation. For example: PET imaging may show false-positive in cases of inflammation and doing PET CT is too expensive to do every year. Doing PET CT is also not recommended for screening, it is only ordered per suspected cancer or metastatic cancer case.

Genetic screening needs to be done once in a lifetime only to detect genetic mutations that cause cancer. However, genetic factors account for only 30% of the causes of cancer. Cancer is caused by daily activities, exposure to carcinogens, unhealthy lifestyle, obesity, smoking, and impure living environment especially because of particle dust causing lung cancer. Gene-cancer screening is valuable when a family member has cancer (generation 1: siblings, parents) and costs are high for screening because it depends on finding multiple genes or only one gene, or some genes for some organs. For example, the cost to do a screening of all gene will be different to do a screening of the breast cancer gene...

The best way to screen and prevent cancer is to have a proper annual checkup with a family doctor. This is the reason why developed countries focus on developing the family doctor system. The Ministry of Health has recently encouraged the development of family doctor system in Vietnam. Family doctor will base on patient’s history of illness, family history of a disease, and health description from patient and from exams to identify patient's risk factors and recommend the patient to do a cancer screening which is accordance with the guidelines of the ASCO or WHO. Meanwhile, the family doctor will also advise patients ways to prevent cancer such as stop smoking, increase activities to lose weight and obesity, restrict to healthy diet, etc. Patients who have unusual symptoms should get consultations from a certain family doctor to know a proper way to look for the cause in order to detect pathology earlier including cancer.