Can a blood test detect cancer before symptoms appear?

Cancer is one of the most prevalent diseases nowadays, affecting approximately 18 million people globally.¹ It is one of the leading causes of death, with around 10 million deaths in 2020.²  However, early diagnosis and treatment are key to a better recovery and a reduced mortality rate. Laboratory tests play an important part in the screening and diagnosis of different types of cancers.  

Laboratory Testing

Laboratory tests consist of examining samples such as blood or other bodily fluids to assess the patient’s health or to look for a specific condition.³ Blood tests are heavily involved in the detection and early diagnosis of cancer, as they offer reliable and accurate information about the patient’s health. There are several tests that can be done on a blood sample in order to aid the diagnosis of cancer. 

• A complete Blood Count (CBC) is done to evaluate the overall numbers of Red Blood Cells (RBCs), White Blood Cells (WBCs) and platelets. In the case of leukaemias, one or more of these types of cells are in higher numbers and are present in their earlier forms in the blood. This test is especially important as some leukaemias can go unnoticed due to the lack of symptoms presented.⁴ 
• A chemistry test involves examining the levels of fats, electrolytes, enzymes and proteins released into the blood by the different organs. Two of the main chemistry tests done on blood are creatinine and Blood Urea Nitrogen (BUN). Creatinine levels are measured to check if the kidneys are functioning properly, as some cancer may affect kidney function. High BUN levels can also signify kidney malfunction due to some types of cancer.

Genetic Testing 

Genetic testing for cancers has become increasingly popular over the last decade. This test involves looking for specific inherited mutations in genes that are found to be associated with an increased risk of developing a certain type of cancer. For example, BRCA1 and BRCA2 testing have become an important aspect to consider when screening for breast, ovarian and even prostate cancers.⁵ In fact, if a mother is diagnosed with breast cancer, it is important that her children are tested for BRCA1 or BRACA2 mutations. As stated previously, these mutations increase the risks of people assigned female at birth (AFAB) developing breast and ovarian cancer, as well as for people assigned male at birth (AMAB) developing breast and prostate cancer.  This genetic testing allows early interventions such as regular screenings, lifestyle changes and risk-reducing surgery. 

In addition to genetic testing, immunophenotyping can be done to examine the antigens present on the cell surface in order to identify the different cells that could potentially be involved in cancer. This test is mostly used to diagnose and determine the stage of leukaemias, lymphomas and myeloproliferative disorders. 

In order to diagnose certain cancers, the number and structure of chromosomes, also known as a cytogenetic analysis, can also be examined. 

Tumour Testing

Another type of testing that is widely used in cancer detection and diagnosis is the tumour markers test. These tests involve examining the presence, activity and levels of specific proteins that might be indicative of the presence of certain cancers. Tumour markers are anything produced by the tumour cells that can give an indication of how aggressive the tumour is, what treatment is optimal for it and whether it is responding to the given treatment. In fact, an increased level of a certain tumour marker is usually suggestive of the presence of cancer. For example, CA-125 is a substance that is increased in certain cancers, such as ovarian cancer.⁶ In addition, beta-2-microglobulin is a protein that is usually found on the cell surface of lymphocytes.⁷ An increase in its levels can be indicative of lymphoma or multiple myeloma. Prostate-Specific Antigen (PSA) is also a protein that can be used as a tumour marker, more specifically for prostate cancer.⁸ However, it is important to note that tumour markers cannot be used alone to make a diagnosis as they face several limitations, the main one being low-specificity. These tests are meant to be used in parallel with other tests in order to establish a more complete clinical picture. 

Other Diagnostic Tests

With research continuously advancing, there are several non-invasive screening and diagnostic tests under development. In fact, combining blood testing with PET-CT scans allows for a more feasible and accurate cancer diagnosis.⁹ Another method still in the works involves using gold nanoparticles mixed with blood to detect a wide variety of cancers in a non-invasive and cost-effective manner.¹⁰

Summary

To sum up, blood tests are an essential part of cancer testing, detection, treatment and prognosis. Blood tests are popular due to their accessibility and how non-invasive they are compared to other testing techniques for cancer, such as biopsies. They can be used to diagnose certain cancers, especially leukaemias, by viewing the cells under the microscope and evaluating any variation in the number of RBCs, WBCs or platelets. Other tests serve as a screening method, such as tumour markers. These tests should therefore be accompanied by other tests such as imaging, CT scans, biopsies and genetic testing. This would allow a more accurate and reliable diagnosis, along with a better prognosis and treatment plan, thus ensuring the best outcome for the patient. Cancer remains one of the leading causes of death nowadays. These mortality rates can be improved with regular screenings, such as mammograms for breast cancer, thus leading to early detection of the disease. This would allow better management of the disease and an improved medical intervention.