An Overview of Cancer Spreading During Chemotherapy

If you or a loved one have been diagnosed with cancer and are going through, or will be starting, treatment, you may wonder if cancer can continue to spread during chemotherapy. 

Although chemotherapy has long been one of the most effective cancer treatments, sometimes tumors can grow, and cancer can spread during treatment. It may mean that it is not effective at controlling the development of the tumor.

This article will detail how cancer can sometimes spread during chemotherapy and the signs that chemotherapy is not working.

Tumor Response to Chemotherapy Treatment - Illustration by Shideh Ghandeharizadeh

Verywell / Shideh Ghandeharizadeh

How Does Chemotherapy Treat Cancer?

In treating cancer, chemotherapy is the use of drugs that kill fast-growing cells. These are non-discriminatory killers—they kill any fast-growing cells in the body, not just cancer cells.

Traditional or standard chemotherapy treats cancer by interfering with cancer cells’ ability to grow and divide. The drugs do so by disrupting their cycle of cell division.

Cell division is when the cells make copies of their chromosomes and split into two. Many molecules, proteins, and genes work together to divide the cell into two, so there are many ways to disrupt this cycle.

In many cases, these drugs are applied to the entire body, called systemic treatment. Systemic chemotherapy can kill cancer cells that have already spread that doctors haven’t found yet. But it can also cause widespread side effects, affecting your digestive tract, immune system, hair, skin, and nails.

Doctors use chemotherapy to treat cancer in three ways:

  • Cure cancer: Kill as much as possible, so it goes away and doesn’t come back
  • Control cancer: Shrink the tumors or stop them from growing and spreading
  • Slow cancer: Slow the growth of cancers and reduce their symptoms (palliative chemotherapy)

Chemotherapy drugs can be administered either through a tube (IV) that delivers liquid medicine into the blood or in pill form. 

Localized Chemotherapy

Some types of cancer can be treated with chemotherapy in one specific area of the body. For example:

  • Bladder cancer may be treated with chemotherapy inside the bladder (intravesically).
  • Cancers of the brain or spinal cord may be treated with chemotherapy directly injected into the spine (intrathecally).
  • Ovarian and other cancers in the abdomen may be treated with chemotherapy directly injected into the abdomen (intraperitoneally). 

Doctors may give chemotherapy drugs in combination with other chemotherapies or different treatment types—like surgery or radiation. It can be given before, during, or after other treatments.

Types of Chemo

Different classes of chemotherapy drugs work to disrupt the cell cycle in various ways. Five major types of chemotherapy encompass the majority of common chemotherapy drugs.

  • Alkylating agents (including nitrosoureas): These agents damage the cell’s genes, so they can no longer function properly. Nitrosoureas are alkylating agents that can travel into the nervous system to treat brain and spinal cancers. An example is Cytoxan (cyclophosphamide).
  • Antimetabolites: These molecules substitute themselves for the normal building blocks of genes (DNA and RNA). They look enough like these molecules to fit into the gene, but they’re different enough that they stop the cell from continuing to build new strands of these genetic molecules. An example is Adrucil (5-fluorouracil).
  • Anti-tumor antibiotics (including anthracyclines): By messing with the proteins the cells use to copy genes, these drugs stop cancer cells from going through the process of copying their genome, stalling their attempt to reproduce. An example is Adriamycin (doxorubicin).
  • Topoisomerase inhibitors: These drugs inhibit the proteins that the cell uses to “unzip” genes to make copies of them (topoisomerases). If the cell can’t copy its genome, it can’t divide. An example is Toposar (etoposide).
  • Mitotic inhibitors: These stop the cells from dividing by damaging the proteins that help the cell reproduce. An example is Taxol (paclitaxel).

A few other chemotherapy drugs act in different ways and don’t fall under these categories. 

Can Cancer Spread During Chemotherapy?

While chemotherapy is one of the oldest and most successful ways of treating cancer, it doesn’t always work. So, yes, cancer can spread during chemotherapy. Spreading could mean the tumor keeps growing, or that the original tumor shrinks, but cancer metastasizes, forming tumors in other areas of the body. 

Advanced cancers, which have spread to other tissues and lymph nodes locally, or have metastasized to other organs, are among the hardest cancers to treat. Chemotherapy may not work to shrink or kill advanced and metastasized cancers.

In these cases, your cancer can keep growing and spreading during chemotherapy treatment. Sometimes, it may require changing the type of chemotherapy to see if it can work better instead. Other times, the goal of chemotherapy may be more palliative—to reduce symptoms from the tumors.

Some cancers spread during chemotherapy because they undergo changes that make them resistant to chemotherapy. These changes can be directly in response to the chemotherapy drugs, or they may have already existed within the tumors. Resistant cancer cells can then be the seeds of new growth of the primary tumor or of distant spread.

Chemotherapy also creates inflammation, and this results in blood vessels becoming more permeable. This can make it easier for the tumor cells to move into the blood or lymphatic vessels and spread.

The cells surrounding the tumor may respond to chemotherapy drugs by releasing chemicals that protect the tumor cells. The development of new blood vessels may also be promoted, and these make it easier for the tumor to grow and spread.

Ways to Tell If Your Treatment Plan Is Working

During chemotherapy treatment, your doctor will order regular scans and blood work to monitor your treatment progress.

Imaging is used in standardized testing called RECIST, which stands for "response evaluation criteria in solid tumors." RECIST is used with solid tumors to assign scores to how the patient is responding to treatment. They take scans to monitor the tumor's size and spread to other parts of the body. 

The doctors then classify the tumor's response to treatment as:

  • Complete response (CR): The tumor has completely disappeared from the scans. 
  • Partial response (PR): The tumor has shrunk by 30% or more from before treatment.
  • Stable disease (SD): The tumor doesn't fall into any of the other categories— cancer has not grown or shrunk during treatment.
  • Progressive disease (PD): The tumor has grown by 20%, or more or more tumors have developed.

When to Speak With Your Doctor About Your Treatment

If your cancer isn’t responding to chemotherapy, talk to your doctor. You’ll want to consider the benefits and risks of the current chemotherapy treatment and discuss what other options may exist.

If the chemotherapy is helping your symptoms, that might be a good enough treatment goal. But if it’s causing more side effects than you’re comfortable with, you may want to consider stopping treatment.

There may be additional treatment options, including clinical trials, that might be a better fit for you. If you’ve tried three different treatment options, it may be time to think about stopping cancer treatment. Talk to your doctor about your options.

If your cancer is advanced or metastatic and doesn’t have a good prognosis, palliative care or changing your treatment approach to focus on your quality of life may be a better option than continuing chemotherapy or other treatments. 


It is possible that cancer can spread while undergoing cancer treatments like chemotherapy. Doctors use regular scans and testing to determine how your chemotherapy treatment is working. If cancer continues to spread, they may recommend changes to the treatment plan. 

A Word From Verywell

Dealing with cancers that spread during chemotherapy or those that have become resistant to treatment can be a very difficult thing to deal with. Try not to bottle up your negative feelings—speak with your care team, family, and friends about your prognosis. Discuss your options with your doctor. 

Frequently Asked Questions

  • How often does cancer spread during treatment?

    How likely cancer is to spread during treatment depends on the type of cancer and how advanced it is when discovered. 

  • What is the most common type of cancer to spread during chemo?

    Advanced cancers of all kinds are the most likely to continue to spread during chemotherapy treatments. Nearly every cancer can metastasize. 

    Common types of metastatic cancer include breast cancer, lung cancer, brain cancer, and bone cancer. Luckily many of these cancers have effective treatment options.

7 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. American Cancer Society. How chemotherapy drugs work

  2. American Cancer Society. How is chemotherapy used to treat cancer?

  3. D'Alterio C, Scala S, Sozzi G, Roz L, Bertolini G. Paradoxical effects of chemotherapy on tumor relapse and metastasis promotion. Semin Cancer Biol. 2020;60:351-361. doi:10.1016/j.semcancer.2019.08.019

  4. National Cancer Institute. Definition of RECIST.

  5. Schwartz LH, Litière S, de Vries E, et al. RECIST 1.1-Update and clarification: from the RECIST Committee. Eur J Cancer. 2016;62:132-137. doi:10.1016/j.ejca.2016.03.081

  6. American Cancer Society. If cancer treatments stop working.

  7. American Society for Clinical Oncology (Choosing Wisely). Care at the end of life for advanced cancer patients.

By Jennifer Welsh
Jennifer Welsh is a Connecticut-based science writer and editor with over ten years of experience under her belt. She’s previously worked and written for WIRED Science, The Scientist, Discover Magazine, LiveScience, and Business Insider.