I am writing this article to answer a question I get from some of my patients about blood tests for cancer. Is there any reliable blood test to detect cancer? Is usually what I am being asked once in a while by my patients.
To answer this question I need first to introduce the notion of Tumor Markers.
These are substances that are produced by the cancerous cells or by the other cells (usually neighboring cells) in the body in response to the detection of cancer or other benign (non-cancerous) conditions.
A tumor is by the definition any abnormal growth of cells, a mass of cells; even a collection of fluid would qualify as a tumor in the world of pathology. Tumors could be benign (not dangerous per se) and malignant (a threatening type of tumor). Also used, there is the term neoplasm, which is another way of saying tumor, in a more academic fashion.
Now, when these cells start to multiply without control, the mass itself starts to produce some chemicals that are called tumor markers. Most tumor markers are made by normal cells as well as by cancer cells. Most of the time, they are produced at a higher number in cancerous conditions. These substances can be mostly found in the blood, but also they show up in urine, stool, tumor tissues or other tissues or bodily fluids of patients with cancer.
To date, based on the listing from National Cancer Institute (USA) website, there are more than 30 tumor markers that are used in clinical care. Some are associated with only one type of cancer, others are associated with two or more cancer types. There is no “universal” tumor marker that can detect any type of cancer. So far. Let’s hope that medicine and oncology with all the grants and pharmaceutical power behind it will find this universal marker in the near future.
The problem with these tumor markers is that sometimes, benign tumors can cause the levels of some tumor markers to increase too. This is a serious limitation to which oncology didn’t find an answer yet. On top of that, tumor markers have not been identified for every type of cancer. I mean, simply put it, there is cancers that do not have tumor markers, do not have something specific to be identified and measured. Cancer is a tricky bastard that is.
Because of these things, tumor markers cannot be used alone to diagnose cancer. They are combined with other tests, of which the BIOPSY is the gold standard in oncology (a pathologist examines the biopsied cells in the lab). Seeing is believing here.
The most common blood tests used in screening for cancer and showed to reduce the cancer deaths are:
- Alpha-fetoprotein blood test
This test is sometimes used, along with ultrasound of the liver, to try to detect liver cancer early in people at high risk of the disease.
- CA-125 test
This blood test, which is often done together with a transvaginal ultrasound, may be used to try to detect ovarian cancer early, especially in women with an increased risk of the disease.
- PSA test
This blood test, which is often done along with a digital rectal exam, is able to detect prostate cancer at an early stage. However, expert groups no longer recommend routine PSA testing for most men because studies have shown that it has little or no effect on prostate cancer deaths and leads to overdiagnosis and overtreatment.
- High-sensitivity Fecal Occult Blood Test (FOBT)
This test has been shown to reduce deaths from colorectal cancer. Colonoscopy and sigmoidoscopy are also done concurrently here and help prevent colorectal cancer because they can detect abnormal colon growths (polyps) that can be removed before they develop into cancer.
It is a blood test used to aid in diagnosis, check whether treatment is working, and assess recurrence for medullary thyroid cancer.
- Lactate dehydrogenase
This test is used to assess stage, prognosis, and response to treatment for tumors like: Germ cell tumors, lymphoma, leukemia, melanoma, and neuroblastoma.
So, unfortunately, the general answer to the question that prompted this article is NO. There are no reliable blood tests that will detect cancer by themselves. There are tests that will raise the alarm for malignancy but these tests are usually done after you have symptoms or are done for screening if you are a high-risk patient for a specific cancer due to your family history (someone in your family died of some cancer at an early age). The symptoms, prior risk, combined with tests (blood or genetic) and imaging will complete the picture for a doctor and a diagnosis will be made and provided.
One word about the genetic testing.
This seems to be the future of cancer screening. Genetic-based testing can tell an individual about their predisposition for certain types of cancer as well act as a tool for the early detection of cancer. These tests are much more accurate than the older generation of cancer markers.