Doctors prescribe chemotherapy to treat various types of cancer, such as breast, ovarian, and prostate cancer. It is vital to assess the effectiveness of chemo to decide if treatment should continue.

Doctors often prescribe chemotherapy to treat various types of cancer. The type of chemo, frequency, and duration of treatment varies based on the specific type of cancer.

Physicians must also monitor someone undergoing chemotherapy to determine if the treatment is working. There are various signs and tests that indicate chemotherapy is working. Doctors may select from different tests to measure the cancer’s response to chemo.

The article below examines how doctors measure the effectiveness of chemotherapy, the tests they use, and how they define the response.

Female receiving chemotherapyShare on Pinterest
Liliya Krueger/Getty Images

Chemotherapy is one of the main treatments for many types of cancer. In the United States, over 1 million people with cancer receive chemo or radiation therapy each year.

It is essential for doctors to know if a person’s chemotherapy is effective. If chemo is not effective, an individual may need to switch to a different type of chemotherapy or treatment.

Someone may have signs that indicate the effectiveness of chemo, such as a decrease in pain or other symptoms. However, the only definitive way to determine if chemotherapy is working involves doing follow-up tests that measure and assess cancer tumors and cells.

Usually, doctors perform tests at different intervals during chemo to assess whether the cancer has become smaller, larger, or stayed the same size. This allows the treatment team to determine whether the current chemotherapy should continue or if the person may need to change to a different treatment.

Tests to measure the effectiveness

Physicians use different tests to measure the effectiveness of chemotherapy. For some people, they may use a combination of tests, which may include:

  • Blood tests: Doctors may order various types of blood tests to measure white and red blood cells, along with platelets. In some types of cancers, the blood counts may indicate the effectiveness of chemo.
  • CT scan: A CT scan creates images of the tissues, bones, and organs. It helps doctors determine the size, location, and shape of cancer. It can provide information on a decrease or increase in cancer.
  • MRI scan: An MRI also creates pictures of the body. Doctors use it to determine tumor size and the tumor’s response to treatment.
  • Tumor markers: Cancer cells produce substances called tumor markers. Tumor markers may increase, stay the same, or decrease in response to chemotherapy. Monitoring tumor markers in the blood may help determine the effectiveness of chemo.

How often healthcare professionals measure the effectiveness of chemotherapy may vary. There is no one standard timeframe to assess chemotherapy. For some people, a doctor may assess treatment if an individual has increased cancer symptoms.

In other instances, the doctor assesses whether chemo is working in the middle of treatment or at the end of the course of chemotherapy. They may also choose to assess the effectiveness every 6–8 weeks.

The frequency of assessment is based on individual circumstances and a doctor should discuss this as part of an individual’s treatment plan.

Doctors generally define the response to chemotherapy by how much, if any, cancer remains in the body. Responses to chemo may include:

  • Complete response: A complete response indicates no detectable evidence of cancer.
  • Partial response: A partial response means cancer has decreased by a certain percentage, but some cancer remains.
  • Stable disease: A stable disease indicates there is no decrease or increase in cancer. The amount of cancer remains the same.
  • Progression: Disease progression means the amount or size of cancer has increased. This may indicate a spread to other areas of the body.

Some doctors may also use the Response Evaluation Criteria in Solid Tumors (RECIST) to assess treatment response for solid tumors. This is a standardized method to evaluate treatment. RECIST uses a percentage of growth or regression to classify the response. However, limitations exist, and the method is not useful for all types of cancer.

Everyone responds differently to chemotherapy and cancer treatment. In some people, chemo may work quickly. In others, it may take longer or not work at all.

In general, a course of chemotherapy often takes between 3–6 months. However, that may vary widely based on individual circumstances and cancer type.

The following are some questions people frequently ask about chemotherapy.

What happens to dead cancer cells?

When chemo or other treatment destroys cancer cells, they no longer multiply. Neutrophils and macrophages, which are immune sentinel cells, take up the dead cancer cells in the body.

Does no side effects mean chemo is not working?

Chemotherapy can cause various side effects, which vary and may depend on the following:

  • a person’s health starting treatment
  • the specific chemo drugs
  • the length of treatment

However, according to the National Cancer Institute (NCI), the extent of side effects does not indicate how well chemo works. It does not mean that chemotherapy is not working if a person has no, or few, side effects.

Cancer resources

To discover more evidence-based information and resources for cancer, visit our dedicated hub.

Was this helpful?

Doctors prescribe chemotherapy to treat many types of cancer. However, everyone responds differently to chemo. Doctors need to assess whether chemotherapy is working to decide if treatment should continue.

Tests to determine if chemo is effective include blood tests, CT scans, and MRIs. In some instances, doctors order more than one test to assess chemo’s effectiveness. A doctor may classify the response to chemo as a complete response, partial response, stable, or disease progression.

Individuals should discuss all treatment options and their potential effectiveness with a healthcare professional.