A team of scientists from the University of Pennsylvania and Croatian National History Museum discovered evidence of fibrous dysplasia, a kind of tumor that causes normal bone to be replaced by tissue that looks more like a sponge.
It's a kind of tumor that still occurs in human bone today.
"They range all the way from being totally benign, where you wouldnt recognize them, to being extremely painful," said David Frayer, a University of Kansas anthropologist and an author on the study, published this week in PLOS ONE. "The size of this one, and the bulging of it, probably caused the individual pain."
The bone containing the tumor was discovered at a site in Krapina, Croatia, which was discovered around the turn of the 20th century and contained almost 900 fossil fragments belonging to several dozen individual Neanderthals.
Scientists speculate the haphazard nature of the bones indicates either the bodies were subject to cannibalism or disturbed by wild animals.
The rib bone contains a large lesion caused by a fibrous dysplasia tumor, revealed by CT and X-ray scans.
Not only are tumors rare in the human fossil record -- any that grew in non-bone tissue would have decomposed over time, whereas bone is far more lasting -- but were likely much more rare among humanoids simply because they lived shorter lives.
"People of that time didn't live as long as they did today; plus, there weren't very many of them compared to the Egyptians and people today," Frayer said. "So finding evidence of tumors and evidence of cancers, is I don't know if I want to say lucky but there isn't a lot of evidence for it."
Living at most into their thirties in a pristine environment, Neanderthals and other humanoids simply didn't develop the kinds of cancers or benign tumors modern humans experience.
Still, the similarity between this tumor and modern disease helps scientists draw a link between human ancestors living thousands of years ago and ourselves.
"It's exactly the same kind of process and in the same place," said Janet Monge keeper of physical anthropology at the University of Pennsylvania Museum. "They lived their lives basically the same way we did and basically with the same problems that we have."