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Cancer recurrence: What do we know?

By Thomas Broom, Vann and Oxford University

Image by allinonemovie,

Cancer recurrence is the term for when cancer comes back after treatment (1). It occurs when cancer is found again after a period of time where it couldn’t be detected (2).

What causes cancer recurrence?

Cancer recurrence usually happens when the original treatment didn’t eliminate all the cancer cells, and so a very small number were left behind (3). This isn’t to say the original treatment didn’t work – it was successful in defeating the vast majority of the cancer. But a very small number of cells may have survived the original treatment (1). These cells don’t appear in tests, but they can grow and become noticeable later. When they do this, they become a recurrent cancer1.

If the original cancer was treated by surgery, a very small number of cells may have remained after the surgery. A microscopic group of cells may have broken away from the main cancer and moved to somewhere where they were missed during surgery (3). If the original treatment involved chemotherapy or radiotherapy, some cancer cells may have avoided the treatment. Or they may have become resistant to the particular drugs that were used (3). These cancer cells could remain and grow into a recurrent cancer at a later time1.

Recent research on cancer recurrence

Understanding what goes on in cancer cells during recurrence is important for research into cancer treatments. Much of the recent research on cancer recurrence has focused on which cancer cells are most involved in recurrence, and how they behave.

Scientists have been looking at a group of cancer cells called cancer stem cells (CSCs). CSCs are a type of cancer cell that can do something unusual – they can become any type of cancer cell in a tumour (4), (5), (6). This means they can start the growth of a tumour by themselves. CSCs are also more resistant to some types of cancer treatment (4), (6), (7).

These features mean that CSCs may often be the cells responsible for cancer recurrence. They may be the cells that are left behind after treatment and the cells that start the re-growth of a tumour, causing the cancer to return (4).

The identification of CSCs as important players in cancer recurrence is great news for cancer research. It has helped scientists understand why cancers can return and is helping to guide the use of existing treatments and research into new cancer treatments for recurrent cancers (7).


Cancer recurrence occurs when cancer comes back after treatment. This happens when a small number of the original cancer cells are left behind after treatment and grow into a recurrent cancer at a later time. A lot of recent research has focused on cancer stem cells – cancer cells that are able to start the re-growth of a tumour. This research is helping to develop new treatment strategies for cancer recurrence.


1. National Cancer Institute, 2020. Recurrent Cancer: When Cancer Comes Back. Available at: [Accessed March 2023].

2. American Cancer Society, 2016. What Is Cancer Recurrence?. Available at: [Accessed March 2023].

3. Cancer Research UK, 2020. Why some cancers come back. Available at: [Accessed March 2023].

4. Peitzsch, C., et al., 2017. Cancer stem cells: The root of tumor recurrence and metastases. Seminars in Cellular Biology, Volume 44, pp. 10-24.

5. Ahmad, A., 2013. Pathways to Breast Cancer Recurrence. ISRN Oncology,

Article ID 290568.

6. Marzagalli, M. et al., 2021. Cancer Stem Cells - Key Players in Tumor Relapse.

Cancers, 13(376).

7. Chang, J. C., 2016. Cancer stem cells: Role in tumor growth, recurrence, metastasis, and treatment resistance. Medicine, 95(S1)

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