Several years ago, biologist Thea Tlsty’s team at the University of California, San Francisco, was studying wound cells in breast tissue. These are adult cells that divide furiously in response to injury, helping to replace those that were damaged. The typical wound cell in the breast has the ability to turn into different kinds of breast cells, each specialized for a different role in the tissue, such as producing milk. But Tlsty’s team stumbled on a subset of repair cells that could do much, much more.

This tiny subset, making up just 1 out of every 10,000 cells in the breast, are pluripotent, meaning that they can be chemically coaxed to turn into a wide range of other cells. “Cells that we could get in the breast, they can make neurons, they can make beating heart cells, they can make bone, cartilage, fat, blood vessel cells — it was amazing,” Tlsty says.

Tlsty published these findings earlier this year, and I just wrote about them for Smithsonian Magazine. The work is exciting because the new stem cells could be used as therapies for a host of diseases, from diabetes to Parkinson’s. But it hasn’t been replicated yet, and until that happens, many scientists aren’t ready to believe it. Why? Because if the study is true, it means that one of biology’s central dogmas is wrong.

“Everybody thought that pluripotency was a condition that went away after you formed your whole body,” Tlsty says. “Because otherwise, why wouldn’t you have an eyeball forming in the middle of your back, right? Or a toenail growing out of your forehead?”

Good point. As it turns out, though, there have been a handful of examples of cells cropping up in tissues where they don’t belong. Tlsty cited a few medical case reports in her paper, and I looked them up. I don’t know if they necessarily bolster her argument, but they’re certainly weird and fascinating.

One of the most common examples of misplaced cells seems to be livers. They grow all over the place. The first reported case, in 1922, described a liver growing on a gallbladder. Since then doctors have found other livers in gallbladders (like the one pictured above), as well as in the thoracic cavity, pancreas, esophagus, and on adrenal glands sitting atop the kidneys. A recent review finds 74 so-called ectopic livers reported in the medical literature, and offers no explanation.

Then there are the errant bones. Take a 2005 report of an 85-year-old woman in the U.K. who went to the doctor for bowel troubles. For a month, she had experienced alternating diarrhea and constipation. The doctors had no idea what it could be, so they peered inside her large intestine. They found a 1.5-centimeter pale brown polyp and sent it to the lab for testing. And what was that polyp? A piece of bone. In her colon. Why was it there? Unclear. Similarly, last year, researchers from Indiadescribed a 16-year-old girl who couldn’t see out of her right eye. The vision loss had started six years earlier, when she suffered “accidental trauma by fist of hand.” Surgeons removed the eye and, a few weeks later, gave her an artificial one. When they analyzed the damaged eye in the lab, they found pieces of adult bone, with marrow and all.

Just one more and then I’ll stop, promise. In 2007, researchers from Japan reported the case of an 11-year-old girl with a brain tumor. She had had the mass since birth and her doctors had been watching it closely throughout her childhood. By age 11, she needed surgery to remove it. Later, researchers analyzed the dissected tissue. And it was totally weird. As one study put it: “The initial histological analysis demonstrated a tumor growing out of what appeared to be nearly normal looking pancreas.” Pancreas. In her brain.

“Pathologists have known for a long time that sometimes the body makes mistakes,” Tlsty says. Her newly discovered stem cells might explain why, or they might not. Either way, it makes me wonder about my own eyes and gut and brain, and all of the misfit cells that may be lurking inside.

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