What happens to cancer cells when they die?

Cancer treatments like chemotherapy kill tumor cells, often by pushing them to self-destruct, shrivel up and quietly die, or less commonly, by triggering a more explosive form of cell death.

But what happens to cancer cells after they die? Typically, the slain tumor cells are recycled in the same way that any other dead cell in the body would be.

When cancer cells meet their demise, their outer membranes usually become compromised. This happens in the “quiet” form of cell death, called apoptosis, a programmed process used to remove unneeded or damaged cells from the body.  

Once the molecular switches that trigger apoptosis are flipped “on,” the dying cell shrinks and bits of its membrane break away in “blebs.” This causes the cells’ internal components to leak out and attract phagocytes, which are immune cells responsible for gobbling up cellular debris.

The summoned phagocytes engulf the dead cancer cells and then break them down into smaller components, such as sugars and nucleic acids, the chain-like molecules found in DNA. Via this process, the dead cancer cells are recycled into components that can later be reused by other cells.

In the case of apoptosis — the type of cell death cancer therapies are traditionally designed to induce — bits of cancer cells are generally recycled in this way rather than excreted by the body, in urine, for example. Cancer therapies can sometimes also trigger other types of cell death, like necroptosis, the “explosive” form of cell death in which tumor cells swell and burst rather than shrinking. Phagocytes also efficiently gobble up this type of dying cell.

However, dying cancer cells don’t always go quietly. Studies suggest that, by releasing various debris that sparks inflammation, the cells can sometimes boost the growth of surviving cancer cells nearby.

This phenomenon, known as the Révész effect, may help explain how some cancers come back after treatment. It was first observed in the 1950s in mice with tumors. More recently, a 2018 study in mice and cells in lab dishes found that radiation and chemotherapy can trigger the release of proinflammatory cytokines, which are molecules released by immune cells that drive up inflammation and can sometimes support tumor growth. 

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