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Chemotherapy (“chemo”) works by destroying cancer cells in your body. Depending on the type and stage of cancer, chemotherapy treatment may target primary tumors or cells that have spread to other parts of your body.

Chemo may also help treat cancer-related pain. A doctor will make specific chemo recommendations based on:

  • the type of cancer
  • its progression
  • the health of the person receiving the chemo

Depending on these factors, chemotherapy may be administered in multiple rounds that are spaced several weeks (or months) apart.

If you or a loved one is in the midst of a chemotherapy treatment plan, you may wonder how you can tell if chemotherapy is working.

The only way to effectively know for sure is through follow-up tests with your doctor. These are given in regular intervals around each round of chemo.

Keep reading to learn how doctors measure and define the effectiveness of chemotherapy.

To treat cancer cells with chemotherapy, your doctor will determine the best cellular phases in which to administer your treatment.

Since cancer cells multiply or divide quickly, chemo may be considered a first line of treatment for more aggressive forms of cancer.

Tests used to measure effectiveness

Throughout your treatment plan, your doctor will need to check your progress to measure the effectiveness of chemotherapy. Depending on the type of cancer and its stage, your doctor may use multiple techniques, such as:

Diagnostic tests What they detect
physical examsidentify visible lumps or lymph nodes that have shrunk in size
blood tests, including a complete blood count (CBC)measure red and white blood cells, platelets, and more
magnetic resonance imaging (MRI), and computed tomography (CT) scansmeasure cancer tumors to see if they’ve shrunk, grown, or spread
tumor marker (biomarker) testsmeasure the amount of cancer cells via blood, tissue, or urine samples

It’s difficult to tell on your own whether chemo is working without taking the above diagnostic tests.

Depending on the type and stage of cancer you have, however, you may notice an improvement in cancer symptoms if the condition is being treated. Examples may include:

  • improved energy levels
  • less pain
  • reduced swelling in lymph nodes

Do chemotherapy side effects mean cancer is improving?

Chemotherapy is notorious for causing side effects, such as:

  • fatigue
  • hair loss
  • nausea

The side effects happen because chemotherapy kills both cancerous cells and healthy ones.

Some people may experience more severe side effects than others. However, side effects are not an effective way to tell that your chemotherapy is working.

Even severe side effects don’t necessarily mean that your treatment is effectively killing cancer cells.

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Before each chemotherapy session, your doctor will perform an assessment to make sure that the treatment is safe to administer. If your CBC counts are too low, for example, your doctor may recommend that you reschedule your treatment for another day.

To determine that chemo is working, your doctor will also need to conduct blood and imaging tests after treatment cycles. Keep in mind that a full treatment cycle includes the days you receive chemotherapy, as well as the weeks you’re in recovery.

When determining the effectiveness of chemotherapy, your doctor will determine how your body is responding to this treatment method. They might declare that you have one of the following responses:

  • Complete response. This means that there’s no detectable cancer left in your body.
  • Partial response. This means that the chemotherapy has helped shrink cancer tumors and prevent the spread of the condition, but cancer cells still exist in your body.
  • Stable disease. This means that chemotherapy hasn’t changed the amount of cancer in your body, and that any tumors you had before haven’t shrunk or grown.
  • Disease progression. In such cases, the cancer has grown and there’s evidence of more disease than before the start of your chemotherapy treatment. Testing may also indicate that cancer has spread to new areas.

In addition to chemo, your doctor may consider other cancer treatments such as:

  • Targeted therapies target specific cancer proteins and receptors to destroy the cancer cells and prevent them from spreading.
  • Immunotherapy uses drugs that boost your immune system, so it’s able to destroy cancer cells before they grow.
  • Hormone therapy stops certain cancers from using hormones needed to grow, such as in the case of breast, uterine, and prostate cancers.

Chemotherapy is administered over the course of several weeks. For example, your doctor might recommend chemo daily for up to 1 week, and then 3 weeks off, according to the National Cancer Institute.

The goal is to target cancer cells when they may be most active while also allowing your body recovery time to build healthy ones.

Still, your exact treatment plan depends on the:

  • type of cancer you have
  • stage of cancer
  • types of chemo drugs used, and whether you’re taking other drugs, such as targeted therapies
  • primary reason you’re taking chemo — for example, to prevent tumor spread or to alleviate pain.
  • how your cancer responds to the treatment
  • how you tolerate the treatment
  • other possible health conditions you may have, such as diabetes or heart conditions

With all of these factors in mind, it’s difficult to predict an exact timeline for when chemotherapy will start working. This treatment may work immediately for some people, while it may take several rounds over the course of many months for others.

The best way to tell if chemotherapy is working for your cancer is through follow-up testing with your doctor. Throughout your treatment, an oncologist will conduct regular visits, and blood and imaging tests to detect cancer cells and whether they’ve grown or shrunk.

It’s important to know that you can’t rely on symptoms alone when determining whether chemo is working. If you start feeling much worse after treatment, however, it’s important to talk with your doctor about your current plan and whether other drugs may help.