It is possible for breast cancer to grow during chemotherapy. However, this suggests that chemotherapy is not working as it should. If this happens, a doctor will reassess a person’s treatment plan.

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Breast cancer is when cells within a person’s breasts begin to grow and divide in an abnormal way. This condition is the most common cancer among females. Breast cancer will affect around 1 in 8 females in the United States, at some point in their lifetime.

Chemotherapy is one of many treatments for breast cancer. In some cases, the cancer may continue to grow and spread to other parts of the body despite the chemotherapy.

This article will explain how this process can unfold, its signs, and how doctors respond to it. It also provides some more general information about chemotherapy and breast cancer.

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As an individual’s breast cancer develops, there is a risk that cancer cells can travel to other body parts. They might do this via the bloodstream or the lymphatic system.

These cells can then prompt cancer to form in other body parts. Doctors call this spread “metastasis.”

According to the American Cancer Society, doctors use chemotherapy to improve survival from breast cancers. It helps to stop the cancer from growing and spreading.

However, breast cancer tumors can still grow bigger during chemotherapy, or potentially spread to the rest of the body. When this happens, it means the chemotherapy has been unsuccessful.

As the National Cancer Institute (NCI) explains, doctors normally treat metastatic breast cancer by attempting to prevent further spread of the disease into more of the organ it is affecting, or other organs.

If metastasis occurs during chemotherapy, treatment might involve the following interventions:

  • changing to a different chemotherapy regimen, such as one that uses other medications
  • adding immunotherapy drugs to the chemotherapy
  • if appropriate, pausing chemotherapy to use a PARP inhibitor

The best option could depend on a number of different factors. Additionally, some people choose to stop their chemotherapy treatment when their breast cancer has reached an advanced stage.

Learn more about what happens if chemotherapy does not work.

If breast cancer spreads to other organs, it can cause symptoms that are related to those organs.

In theory, breast cancer can spread to any body part, with or without chemotherapy. However, the NCI notes that some organs are more common sites of breast cancer metastasis. These include:

  • the brain
  • the liver
  • the lungs
  • bones

These different metastatic breast cancers will manifest in different ways. For instance, bone metastases could cause bone pain or fractures.

Brain metastases could lead to headaches, dizziness, or seizures.

Lung metastases may cause shortness of breath, while liver metastases might induce jaundice.

Learn more about how breast cancer spreads.

To know if chemotherapy is working, a person can continue with follow-up visits and testing with an oncologist.

Doctors can perform blood tests and imaging tests to see if chemotherapy is working. These tests can detect cancer cells to determine if they have shrunk or continued growing.

During chemotherapy, there is a greater risk of developing a serious infection. This can be life threatening. A person should seek medical advice as soon as possible if they experience the following symptoms:

  • fever of 100.5ºF (38ºC) or higher
  • cough and sore throat
  • chills
  • diarrhea
  • ear pain
  • rash
  • swelling or inflammation at the site the catheter enters the body
  • cloudy or bloody urine
  • ear pain
  • headache
  • sinus pain
  • stiff or sore neck

As breast cancer develops, there is a risk of it spreading to other parts of the body. This is called metastasis. Although unlikely, this can occur during chemotherapy, indicating a lack of successful treatment.

If chemotherapy is not working, a doctor will reassess a person’s treatment plan.

A person should speak with an oncologist if they have any questions or concerns about how their treatment is going to affect them.