Breast cancer is one of the most diagnosed cancers in the European Union, with around 380,000 cases per year, accounting for approximately 13.8% of all cancer diagnoses*. Breast cancer is much more common in women, with 99% of cases affecting women, but it can still occur in men.
Cancer is divided into stages and grades based on the size of the tumor, involvement of the tumor in nearby lymph nodes, and the presence of metastases. Stages range from 0 to IV, with IV being the most severe. Cancer grades range from I to III based on the appearance of the cancer cells, with grade III indicating high levels of tumor abnormalities and aggressiveness.
While stage IV breast cancer (also known as metastatic or advanced stage breast cancer) is incurable, it can be managed with various treatment approaches aimed at controlling the disease. With the right dose and type of treatment administered, patients may be able to prolong their survival and alleviate the severity of side effects from cancer and related therapies.
In this article, we look at how it is based on blood tumor marker tests play a role in the management of stage IV breast cancer. In particular, the types of markers available, their functions and limitations, and their clinical applications.
Blood-based biomarkers are substances that can be detected in blood. They are produced by breast cancer cells or normal cells in response to breast cancer. These markers include proteins, enzymes or genetic material, and their activity levels in the blood of a cancer patient can provide valuable information on the progression of the disease and their responses to treatment.
This information is used by doctors to tailor treatment journeys for patients, including changing certain methods in favor of others, or changing the dose and frequency of medications and therapies for better treatment outcomes.
A major advantage of blood-based tumor marker testing in disease monitoring is its ease and minimally invasive nature. The test involves taking a blood sample from the patient and may be included as part of routine check-ups. Compared to traditional monitoring methods, such as imaging techniques or tissue biopsies, it significantly reduces patient discomfort and risk.
Common blood-based tumor markers
Established and evolving clinical data support the use of several blood-based tumor markers for monitoring breast cancer response.
CA 15-3
This is a blood-based tumor marker often used in monitoring advanced or metastatic breast cancer, particularly in the areas of disease progression and response to treatment. CA 15-3 is a glycoprotein that is produced by breast cancer cells, and measuring its levels in patients' blood over time can provide insight into changes in tumor burden and response to therapy.
However, CA 15-3 has its limitations, such as lack of specificity and variable sensitivity.
While CA 15-3 levels can be elevated in the blood of breast cancer patients, they can also be elevated in other non-cancerous conditions, such as liver disease, benign breast conditions, and other types of cancer. Lack of specificity may result in an inaccurate assessment of disease progression.
Furthermore, while CA 15-3 is suitable as a tumor marker for advanced-stage breast cancer, it is not suitable for testing in patients with early-stage or localized cancer. When used in early-stage testing, false-negative results can occur when the marker fails to detect the presence of cancer or changes and developments in disease status.
CA 27.29
CA 27.29 is another blood-based tumor marker used in breast cancer monitoring. As a variant of the CA 15-3 protein, CA 27.29 is particularly useful in monitoring patient response to therapy and detecting disease recurrence in patients with advanced breast cancer.
This is due to the increased sensitivity of the marker in cases where there is a large tumor burden or metastatic spread. CA 27.29 levels also tend to be associated with more aggressive subtypes of breast cancer, such as those that include hormone receptor-positive and HER2-negative tumors.
However, CA 27.29 has its limitations. Like CA 15-3, CA 27.29 has no specificity and can be elevated in other non-cancerous conditions, including benign breast conditions, and its variability in sensitivity can lead to false-negative results also when it fails to detect changes in cancer status.
TK1
Thymidine Kinase 1 (TK1) is a promising blood-based tumor marker for breast cancer monitoring. As an enzyme involved in DNA synthesis and cell proliferation, measuring TK1 activity levels in the blood can provide valuable insights into cancer cell behavior and tumor aggressiveness.
Elevated levels of TK1 have been observed in the blood of breast cancer patients. This is because as cancer cells divide and multiply, they require increased DNA synthesis, a process in which TK1 plays a key role.
By serially measuring TK1 levels over time, changes in tumor burden and patient responses to therapy can be detected. Elevated TK1 levels may indicate an aggressive tumor and a poor response to treatment, while decreased TK1 levels may suggest a positive response.
The limitation of TK1 lies in its status as an emerging biomarker. While the enzyme is still being evaluated, further research is required to fully establish its clinical utility and standardize its use in breast cancer monitoring.
However, it shows good potential in providing valuable information on the activity of cancer cells. When used in combination with other assessments and imaging techniques, it is likely to increase the accuracy and reliability of disease monitoring.
Choosing the most appropriate tumor marker for disease monitoring
Among the three blood-based tumor markers introduced, CA 15-3 and CA 27.29 are most frequently used in breast cancer monitoring. This is due to extensive published research on their clinical utility. However, while TK1 is an emerging tumor marker, its association with cell proliferation has shown promise in disease progression and treatment response monitoring.
Ultimately, the choice of tumor marker to use may depend on factors such as the specific clinical context, the stage and subtype of breast cancer to be monitored, and the availability of testing. The individual characteristics of the patient must also be taken into account. If you want to determine the most appropriate approach for your situation, you should consult with health care professionals.
