Is Chemotherapy Working?
By Sarah Friend, MD
One of the most common questions I hear from patients is, “How do we know if my chemotherapy is working?” The answer depends on why chemotherapy is being given. Chemotherapy is used for different reasons, and success is measured differently depending on the stage of cancer and the goal of treatment.
Chemotherapy Before Surgery (Neoadjuvant Chemotherapy)
Sometimes chemotherapy is given before surgery to shrink a tumor. This is called neoadjuvant chemotherapy.
Like chemotherapy given after surgery, the primary goal of neoadjuvant chemotherapy is to reduce the risk of the cancer coming back. The difference is that when chemotherapy is given before surgery, doctors can actually see how the cancer responds to treatment. During treatment, your healthcare team may monitor the tumor with physical exams, mammograms, ultrasound, or MRI to see whether it is shrinking.
The best possible outcome is called a pathologic complete response (pCR). This means that when the breast tissue and lymph nodes are removed during surgery, no remaining invasive cancer is found under the microscope. Achieving a pCR is associated with an excellent prognosis for many patients, particularly those with triple-negative or HER2-positive breast cancer.
Even if a pCR is not achieved, chemotherapy may still be very effective. Significant tumor shrinkage can make surgery easier and, like adjuvant chemotherapy, helps reduce the risk of the cancer returning.
Chemotherapy After Surgery (Adjuvant Chemotherapy)
When chemotherapy is given after surgery, it is called adjuvant chemotherapy.
The goal is the same as neoadjuvant chemotherapy—to reduce the risk of the cancer returning. However, because the tumor has already been removed, there is no visible cancer left to measure. Instead, chemotherapy is given to destroy microscopic cancer cells that may still be present but are too small to detect with today’s imaging tests.
Because there is no measurable tumor to follow, doctors cannot determine whether chemotherapy is working during treatment. Instead, success is measured over time.
Simply put, chemotherapy has done its job if the cancer never returns. While no treatment can eliminate the risk of recurrence completely, adjuvant chemotherapy significantly lowers that risk for many patients.
Chemotherapy for Metastatic (Stage IV) Cancer
For people living with metastatic breast cancer, chemotherapy is used to control the cancer, relieve symptoms, improve quality of life, and help patients live longer.
Unlike early-stage breast cancer, metastatic disease can usually be measured on imaging studies. Your oncologist will typically order CT scans, PET scans, bone scans, or MRI every two to four months, depending on your individual situation, to monitor how treatment is working.
Scan results generally fall into one of three categories:
- Cancer is shrinking. This is the ideal outcome and shows that treatment is effectively reducing the amount of cancer.
- Stable disease. The cancer has not grown or shrunk significantly. Although this may sound disappointing, stable disease is often considered a successful result because it means treatment is keeping the cancer under control.
- Progressive disease. The cancer has grown or new areas of cancer have appeared. When this happens, your oncologist will usually discuss changing to a different treatment.
The best possible response is called no evidence of disease (NED). This means there is no visible cancer on imaging studies. While NED does not always mean a person is cured, especially in metastatic breast cancer, it is an outstanding response to treatment.
What About Tumor Markers and Blood Tests?
Many patients ask whether blood tests can tell if chemotherapy is working.
Sometimes oncologists use tumor markers, such as CA 15-3, CA 27-29, or CEA, particularly in metastatic breast cancer. These tests may provide additional information when interpreted alongside symptoms, physical examinations, and imaging. However, tumor markers alone should not determine whether treatment is changed because they can fluctuate for many reasons.
You may also hear about circulating tumor DNA (ctDNA) tests, such as Signatera®. These tests look for tiny amounts of tumor DNA circulating in the bloodstream and are an exciting area of ongoing research.
At this time, ctDNA testing is not considered routine standard of care for most patients with breast cancer. While these tests may be appropriate in select situations or clinical trials, researchers are still studying how best to use the results to guide treatment decisions.
The Bottom Line
The question, “Is chemotherapy working?” does not always have a simple answer because it depends on the goal of treatment.
For both neoadjuvant and adjuvant chemotherapy, the ultimate goal is the same: to reduce the risk of the cancer returning. The difference is that when chemotherapy is given before surgery, doctors can directly observe how the tumor responds to treatment. When chemotherapy is given after surgery, there is no visible cancer left to measure, so its success is determined over time by whether the cancer stays away.
For metastatic breast cancer, treatment is monitored with regular imaging. Chemotherapy may be considered effective if the cancer shrinks, remains stable, or, in the best-case scenario, becomes undetectable on scans.
Understanding why you are receiving chemotherapy can help you better understand how your oncology team measures success. If you are ever unsure how your treatment is being monitored or what your scan results mean, don’t hesitate to ask. Knowing the goals of your treatment can help you feel more informed and confident throughout your cancer journey.
