Breast cancer is a complex disease that requires careful monitoring throughout its course to guide treatment decisions and assess treatment efficacy. Various methods can be employed to monitor the progression of breast cancer, including imaging techniques, biopsies, and blood-based biomarkers. A combination of these methods can also be used for medical practitioners to tailor treatment journeys for different breast cancer patients, whether their goal is to prolong survival, prevent cancer recurrence, or ease the severity of treatment side effects.

In this article, we look at each of these monitoring methods and provide some examples of each one. From the use of CT scans and MRIs to tissue biopsies and biomarker tests, we will examine the advantages and limitations of each modality.

Imaging techniques

The use of imaging techniques to monitor breast cancer progression is common, from the use of PET and CT scans to using MRIs. As the standard method of treatment evaluation, imaging can be used to evaluate the breast tissue itself, lymph nodes in the axilla (armpit) region, bones, and organs in advanced-stage breast cancer where cancer cells have spread beyond the breast.

Using imaging techniques to monitor cancer progression offers several advantages. It is non-invasive, and certain techniques allow for a comprehensive evaluation of the entire body, which is particularly useful in identifying distant metastases. However, breast cancer imaging often comes at a high cost, and unwanted radiation exposure from PET and CT scans should be considered.

PET scans

Positron Emission Tomography (PET) scans use a small amount of radioactive material and a specialised camera to detect metabolic activity in tissues. PET scans are effective in evaluating the spread of breast cancer to other parts of the body, such as the bones, liver, or lungs. This information can guide medical practitioners in making tailored treatment strategies to optimise outcomes.

CT scans

Computed Tomography (CT) scans use X-rays and computer processing to create detailed cross-sectional images of the body. It is not commonly used in breast cancer monitoring, but CT scans can also be employed in instances of distant metastases or in evaluating treatment responses in advanced cases.

MRIs

Breast Magnetic Resonance Imaging (MRI) uses a magnetic field and radio waves to create detailed images of the breast, and it is effective in evaluating the extent of the cancer due to its high sensitivity. With MRI, medical practitioners can continually monitor disease progression and treatment response by assessing tumour size and detecting hidden tumours.

Biopsies

A biopsy is a medical procedure in which a sample of tissues or cells is collected from the breast for examination and analysis. As biopsies provide direct access to the tumour tissue, they can provide accurate information about the tumour’s characteristics, allowing medical practitioners to determine the type, grade, and molecular subtype of the tumour.

Expression levels of Ki-67, HER2, and HR are assessed through biopsy samples, which can be used to determine tumour aggressiveness and guide targeted therapy choices.

Ki-67

Ki-67 is a protein marker commonly assessed through immunohistochemistry (IHC) in breast cancer biopsies. To assess Ki-67 expression, a tissue biopsy is obtained from the breast tumour or metastatic site. In some cases, a hollow needle can be used to extract small tissue samples from the breast mass. In others, where a larger tissue sample must be obtained, a surgical biopsy may be performed.

As Ki-67 is expressed in actively dividing cells, its expression indicates the level of cell proliferation or the growth rate of cancer cells, which can be used as a measure of disease aggressiveness and status. High Ki-67 expression recorded over time suggests a more rapidly proliferating tumour or a lack of response to existing treatment methods.

HER2

Human Epidermal Growth Factor 2 (HER2) is a protein that is overexpressed in approximately 15-20% of breast cancers. HER2 overexpression is associated with more aggressive tumour behaviour, and it can be detected through immunohistochemistry (IHC) or fluorescence in situ hybridisation (FISH) tests performed on biopsy samples.

Monitoring HER2 status during treatment provides information on disease progression and helps medical practitioners assess treatment response. If the tumour shows resistance to targeted therapies or if there is a change in HER2 status and expression, treatment adjustments can be made.

HR

Hormone Receptors (HRs) such as Estrogen Receptors (ERs) and Progesterone Receptors (PRs) can also provide insight into breast cancer progression. Biopsies are performed to obtain tissue samples to be examined, which determines the absence or presence or ERs and PRs. This is called the HR status.

HR status determines tumour aggressiveness, with HR-positive breast cancers typically associated with lower aggression compared to HR-negative breast cancers. In ongoing monitoring of the disease, HR status can be obtained in intervals for medical practitioners to evaluate the effectiveness of treatment.

Blood-based biomarkers

Blood-based biomarkers are measurable characteristics or molecules that are present in the blood, and they can be used to monitor and evaluate breast cancer disease progression and treatment response. These biomarkers can be enzymes, proteins, or fragments of genetic materials. Common biomarkers include CA 15-3, CA 27.29, and TK1.

Using blood-based biomarkers offer several advantages. As samples can be retrieved with just a blood draw, it is minimally invasive to decrease patient risk and discomfort. Biomarker testing is also relatively accessible due to its low cost, making them a suitable monitoring method as samples can be taken easily and repeatedly over time. However, many biomarkers are not specific to breast cancer and their activity and levels can be elevated in other conditions as well, which can pose issues related to accuracy.

CA 15-3

Cancer Antigen (CA) 15-3 is a protein that is sometimes elevated in the blood of patients with breast cancer. As a subtype of the mucin 1 (MUC1) protein, which is over-expressed in breast cancer cells, CA 15-3 can be used as a tumour marker to monitor disease progression in patients with advanced breast cancer. By taking measurements of CA 15-3 levels over time, medical practitioners can track changes in tumour burden.

CA 27.29

Cancer Antigen (CA) 27.29 is another subtype of the mucin 1 (MUC1) protein. Like CA 15-3, it can be used in blood-based biomarker testing to monitor disease progression in advanced breast cancer patients. Rising CA 27.29 levels may indicate disease progression, while decreasing or stable levels may suggest a positive response to treatment.

TK1

Thymidine Kinase 1 (TK1) is an enzyme involved in cell proliferation and DNA synthesis. In breast cancer, increased TK1 activity and levels can be observed due to the rapid division of cancer cells. TK1 can be measured using specific assays, and its activity levels can reveal insights into cancer progression and patient response to treatment. For example, elevated TK1 in the blood may indicate increased tumour burden or cancer cell proliferation, and monitoring its levels can provide information on disease progression.

Finding the right breast cancer monitoring method

Choosing the most suitable monitoring method for breast cancer depends on various factors. These include your current treatment plan, the stage and grade of cancer you have, treatment availability and accessibility, your biological characteristics, and your comfort levels. Most likely, the decision will be made with the guidance of your oncologist or healthcare provider, who will be able to consider your unique circumstances and the specific goals of monitoring, which can range from prolonging survival to easing the side effects of treatment.