Researchers at Harvard-affiliated Boston Children’s Hospital have, for the first time, visualized the origins of cancer from the first affected cell and watched its spread in a live animal. Their work, published in the Jan. 29 issue of Science, could change the way scientists understand melanoma and other cancers and lead to new, early treatments before the cancer has taken hold.

“An important mystery has been why some cells in the body already have mutations seen in cancer, but do not yet fully behave like the cancer,” says the paper’s first author, Charles Kaufman, a postdoctoral fellow in the Zon Laboratory at Boston Children’s Hospital. “We found that the beginning of cancer occurs after activation of an oncogene or loss of a tumor suppressor, and involves a change that takes a single cell back to a stem cell state.”

That change, Kaufman and colleagues found, involves a set of genes that could be targeted to stop cancer from ever starting.

The study imaged live zebrafish over time to track the development of melanoma. All the fish had the human cancer mutation BRAF^V600E — found in most benign moles — and had also lost the tumor suppressor gene p53.\

Kaufman and colleagues engineered the fish to light up in fluorescent green if a gene called crestin was turned on — a “beacon” indicating activation of a genetic program characteristic of stem cells. This program normally shuts off after embryonic development, but occasionally, in certain cells and for reasons not yet known, crestin and other genes in the program turn back on.

“Every so often we would see a green spot on a fish,” said Leonard Zon, director of the Stem Cell Research Program at Boston Children’s and senior investigator on the study. “When we followed them, they became tumors 100 percent of the time.”

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