Monitoring Your Response to Metastatic Breast Cancer Treatment

Determining if your disease is managed or progressing

Your response to metastatic breast cancer treatment will be monitored closely by your healthcare provider, who will use different tests to see if your disease is under control or has progressed.

Tumors can change over time, breast cancer treatments may work better for some people than others, and treatment can affect your cancer differently at different times throughout your disease course. 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.

Senior woman sitting on hospital bed
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How Tumors Can Change

Cancer cells often change to evade the immune system. With breast cancer, 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 late.

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 metastasis in a different location, does not.

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


Repeat biopsies aren't always done, but they can be if your healthcare provider thinks that the characteristics of your tumor may be different than when you were diagnosed.

Imaging Studies

The imaging scans your healthcare provider recommends will depend on many factors, including the location of your tumors and the treatments used.

Common tests include:

  • X-rays: These may be done to identify 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.
  • CT scans: A computed tomography (CT) scan may be done to examine your abdomen, pelvis, chest, or head.
  • MRIs: Magnetic resonance imaging (MRI) may be done to get a detailed visual image of areas where there may be metastases.
  • PET scans: Unlike CTs and MRIs, which primarily examine structural features, a positron emission tomography (PET) scan examines cell function, highlighting actively growing tissues such as cancer cells. PET scans are helpful in distinguishing areas such as scar tissue and fibrosis from actively growing malignant tumors.


While imaging tests are an important part of the monitoring process, they have limitations.

Some important issues 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 your tumor size may not be apparent on a scan until a few weeks, or even months after your treatment is completed.
  • Scans aren’t perfect: All scans can potentially mistake normal tissue for an abnormality. The more tests you have, the more likely this is to occur.
  • Scans can’t tell you if a “spot” is “growing”: Sometimes it can be difficult to determine if a “spot” represents a tumor that's growing or simply scar tissue left by cancer treatment.
  • 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 than it had been previously. 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.

A change in the levels of these markers can be delayed by several weeks after a tumor increases or decreases in size.

Tumor marker tests are not perfect. Not all breast cancers cause elevations in biomarkers, and these biomarkers can be elevated 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 healthcare provider 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 to 90% of people with metastatic breast cancer, but only 30% of people with early-stage breast cancer. Levels of this biomarker tend to be particularly high with bone or liver metastases. CA 15-3 may be measured to assess your cancer treatment response, 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 it 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. Elevations may remain for a significant amount of time (two to three months) even after cancer has been effectively treated. Your healthcare provider 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 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. With metastatic breast cancer, 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.
  • 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.
  • Consider the progress you have made in treatment and diagnosis, and try to remember that the fact that you're getting treatment is good for your health.

Breast Cancer Doctor Discussion Guide

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

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4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Lindström LS, Karlsson E, Wilking UM, et al. Clinically used breast cancer markers such as estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 are unstable throughout tumor progression. J Clin Oncol. 2012;30(21):2601-8. doi:10.1200/JCO.2011.37.2482

  2. Sharma M, Gogia A, Deo SSV, Mathur S. Role of rebiopsy in metastatic breast cancer at progression. Curr Probl Cancer. 2018; doi:10.1016/j.currproblcancer.2018.12.001

  3. Gold LS, Lee CI, Devine B, et al. Imaging Techniques for Treatment Evaluation for Metastatic Breast Cancer [Internet]. Rockville (MD): Agency for Healthcare Research and Quality (US); 2014 Oct. (Technical Briefs, No. 17.) 

  4. Cancer.NET Topic #4: Follow-up Tumor Marker Tests and Imaging Tests for People Treated for Breast Cancer.

Additional Reading

By Lynne Eldridge, MD
 Lynne Eldrige, MD, is a lung cancer physician, patient advocate, and award-winning author of "Avoiding Cancer One Day at a Time."