Video: Rare Observation of How Cancer Spreads

While a tumor may be composed of billions of cells, only a tiny fraction break away and spread.

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By Tina Hesman Saey, Science News

SAN DIEGO—A growth factor helps cancer cells get a move on, a new study shows.

Even a modest-size tumor may be composed of billions of cells, but only a tiny fraction ever break away to migrate to other parts of the body. Details of what makes some cancer cells metastasize, as the movement is called, have not been well understood because it is difficult to find and observe such a rare event.

“We’re looking at a needle in a haystack, but it’s a moving needle, so that makes it that much harder,” said Erik Sahai of Cancer Research UK’s London Research Institute, who conducted the study and presented the work during the American Society for Cell Biology annual meeting.

Sahai and colleagues developed a microscopy technique that could allow them to watch breast cancer cells break away from the main tumor in mice. The team genetically engineered the cancer cells to see whether the cells were getting a signal from transforming growth factor-beta (TGF-beta), a message other evidence indicated might be necessary for metastasis.

Single cells that left the main tumor were getting a signal from TGF-beta, the images showed (the cells glow blue when they receive the signal). But cells that migrate in groups weren’t prodded by TGF-beta. The team also found that clumps of cells can move into the lymphatic system and spread locally, but can’t enter the bloodstream and move into lungs the way single cells do.

Single cells will continue their nomadic ways as long as the TGF-beta signal is on, Sahai said. The data don’t have any immediate clinical application, but could one day help doctors stop cancer in its tracks.

Breast cancer cells (shown in green) individually peel off from the main tumor when they get a "go" signal from a type of growth factor called TGF-beta. Cells can also move in clumps, but that migration is not controlled by TGF-beta, shows a new study presented at the American Society for Cell Biology annual meeting. Immune cells called macrophages are shown in red and connective tissue appears in cyan and magenta.

Credit: Erik Sahai - Cancer Research UK

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