A particularly high-profile case covered by The New York Times featured a 66-year-old man who visited clinics in China and South America to receive stem cell injections into his spine to attempt to fix residual neurological deficits he lived with after a stroke. He developed incontinence, paralysis and lower-back pain, and doctors subsequently revealed a growth on his spinal cord, formed from the stem cell injections. The growth didn’t have any classic cancer-related mutations, so it’s difficult to formally define it as a malignancy, but this and scattered other cases, such as the example of a 13-year-old boy in Israel who developed growths in his brain after an ill-advised attempt to treat his rare genetic disease with stem cells, serve as a stark warning to those wanting to try these treatments.
As a cancer research scientist, I’m worried. Stem cells in the lab form tumors called teratomas when put into mice. Indeed, it’s one of the tests frequently used to prove that we have made genuine stem cells. Last year, researchers at Harvard showed that stem cells grown in the lab frequently acquire mutations in the notorious p53 gene, which is mutated in over 50% of cancers. Additionally, they showed that these mutated cells had a growth advantage, progressively outcompeting the non-mutated cells in the cultures. Many stem cell therapies in development involve periods of culture in the lab and sometimes genetic manipulation before injecting them into the participant, so there are significant concerns as to whether this might increase the likelihood that they can cause cancer.