Monitoring Your Response to Metastatic Breast Cancer Treatment

Determining if your disease is managed or progressing

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Your response to metastatic breast cancer treatment will be monitored closely by your doctor, who will use many tests to see if your disease is being managed or has progressed. Some of these imaging studies and lab tests are used when someone is diagnosed with early-stage or metastatic (stage 4) breast cancer, whereas others are primarily used to monitor the treatment of advanced disease.

Tumors can change over time, essentially making successful treatment a moving target. Furthermore, breast cancer treatments may work better in some people than others, and even better at certain points of one's disease course than another. Your oncologist will work diligently to stay on top of your response to treatment to make sure that your regimen is as effective as it can be.

How Tumors Can Change

We often think of cancers as unchanging, but that is not the case. Cancers are continually adapting to their surroundings, often producing new proteins to evade your immune system and altering their appearance to aid in their survival.

Aside from the molecular characteristics of a tumor changing, receptor status can change too. For example, a tumor may have been estrogen-sensitive when you were first diagnosed, but it may be estrogen receptor-negative when it reappears in your lung. A tumor may be HER2-positive when first diagnosed, but HER2-negative later. These changes are common, with up to 5 percent of HER2-positive tumors becoming HER2-negative later on.

Tumor heterogenicity is another important point of consideration. Rather than being a mass of all identical cells, different parts of a tumor may have different characteristics than others. Sometimes one portion of a tumor overexpresses HER2, while another section of a tumor, or a metastasis in a different location, does not.

This is a simplistic description of what happens, but it helps set the stage as to why every breast cancer is unique.

Changes in tumors are what account for the resistance to treatments such as hormonal therapies, targeted therapies, and chemotherapy that sometimes happen over time.

Biopsies

One of the most important first tests in metastatic breast cancer monitoring is a biopsy of your cancer. Your doctor will do this to determine whether the sample is metastatic breast cancer or an unrelated tumor. However, the most important reason for a biopsy, or a “re-biopsy,” is to determine how your cancer may have changed since the time you were first diagnosed.

Imaging Studies

The imaging scans your doctor recommends will depend on many things, from the location of your tumors to the treatments used. Common tests include:

  • X-rays of areas in which you’re suspected of having bone metastases
  • Bone scans: This study involves injecting a radioactive tracer, which is then evaluated with imaging. Bone scans can be helpful in evaluating bone metastases as well.
  • CT scans: A computed tomography (CT) scan may be done to look at your abdomen, pelvis, chest, or head.
  • MRIs: Magnetic resonance imaging (MRI) may be done to get a more accurate look at any metastases in your brain or other regions of your body.
  • PET scans: Unlike CTs and MRIs, which primarily look at structural features, a positron emission tomography (PET) scan looks at the function of cells in your body, highlighting actively growing tissues such as cancer cells. In addition to helping to evaluate the extent of your cancer, PET scans are helpful in distinguishing areas such as scar tissue and fibrosis from actively growing malignant tumors.

Limitations

While imaging tests are an important part of the monitoring process, they are not without their issues. It's important to understand not only their pros, but their cons. Among some important ones to be aware of:

  • Changes on a scan can be delayed: If you just finished a treatment such as chemotherapy, you may feel discouraged if a scan shows that your tumor hasn’t changed in size. It’s helpful to understand that changes on an imaging test can take time to show up. For example, a decrease in tumor size due to treatment may not show on a scan until a few weeks or even months after your treatment is completed.
  • Scans aren’t perfect: No matter what type of scan you have, there is a chance it will “find” something that would otherwise not be a problem. The more tests you have, the more likely this is to occur. An example includes the many benign liver nodules found on abdominal CT scans that can be hard to distinguish from cancer.
  • Scans other than PET scans can’t tell you if a “spot” is “growing”: It may be difficult on a test such as a CT scan to determine if a “spot” represents a tumor that's growing or simply scar tissue left by cancer treatment. PET scans can help distinguish actively growing cancers from benign processes, but can also have false positives, which are areas of concern that turn out to be nothing.
  • A small change in the size of a tumor may be meaningless: Some people become discouraged if a tumor appears to be a centimeter larger on a scan than it had been on a previous one. If you are faced with something like this, ask your radiologist about the limitations of the particular imaging you had. In some cases, a tumor that may appear to be larger or smaller on a scan has not changed in actual size.

Tumor Marker Tests

Tumor markers, or biomarkers, are proteins that are either secreted by a tumor or by the body in response to a tumor. Blood tests to check for these proteins may be done to follow your progress with metastatic breast cancer.

However, a change in the levels of these markers, just as with scans, can be delayed by several weeks after a tumor increases or decreases in size.

As with imaging tests, these tests are not perfect. Not all breast cancers cause elevations in biomarkers, and when they are elevated, it may be due to a condition other than cancer.

These tests are rarely used alone to monitor the progress of breast cancer and are most helpful when the levels are followed over time.

Tumor markers your doctor may measure include:

  • Cancer antigen 15-3 (CA 15-3): CA 15-3 is a protein made by breast cancer cells. It can be found in 50 percent to 90 percent of people with metastatic breast cancer, but only 30 percent of people with early-stage breast cancer. Levels of this biomarker tend to be particularly high in those who have bone or liver metastases. CA 15-3 may be measured to assess the response of your cancer to treatment, but a change in the level may not occur for several weeks (often four to six) after a tumor either progresses or responds to treatment.
  • Cancer antigen 27.29 (CA 27.29): CA 27.29 is a protein that is produced by a gene known as MUC-1 and is found on the surface of some breast cancer cells. In contrast to the other markers, CA 27.29 is the only protein that specifically indicates the presence of breast cancer cells. Though this test is not currently used to monitor recurrence in women who've had early-stage breast cancer, it’s thought that an elevation may occur around five months before a person is otherwise aware that their cancer has recurred. As with CA 15-3, conditions other than breast cancer can cause elevations in this protein, and elevations may remain for a significant amount of time (two to three months) even after cancer has been effectively treated. Your doctor may order either a CA 15-3 or CA 27.29 test, but not usually both.
  • Carcinoembryonic antigen (CEA): CEA is a nonspecific protein that may be elevated in people with cancer as well as in response to several other conditions, including smoking.
  • Circulating tumor cells: Monitoring blood for circulating tumor cells (entire cells or parts of tumor cells that have broken off and entered the bloodstream) is a newer approach for evaluating and following metastatic cancer. Though still mostly investigative, one test has now been approved for use in women with metastatic breast cancer.

Waiting for Test Results

Most people will feel some level of anxiety while waiting for the results of scans or laboratory tests, regardless of when they were performed in the course of treatment. With metastatic breast cancer, in particular, you'll have many test results to await.

You’re not alone if your mind conjures up (and fixates on) potential scenarios of what the results may be—and more importantly, what they could mean.

You can do several things to cope during these waiting periods:

  • Ask about the timing of your results and how you'll be receiving them.
  • Be picky about the timing of your scan. If it's done earlier in the day, it might get read by the end of the day, saving you stress overnight. Being tested earlier in the week might spare you the stress of waiting the weekend for the news.
  • Ask somebody to join you when you go to the exam as a distraction.
  • Watch a funny movie, go to a comedy show, or do anything that will make you smile.

Breast Cancer Doctor Discussion Guide

Get our printable guide for your next doctor's appointment to help you ask the right questions.

Doctor Discussion Guide Woman
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