A fossilized foot bone found in South Africa is the oldest evidence yet that ancient humans suffered from cancer, scientists say.

The bone, which dates back about 1.7 million years, shows signs of osteosarcoma, or bone cancer. 

Scientists can't say for certain which exact category of early human ancestor the bone belongs to. It was recovered from the Swartkrans cave site, near Johannesburg.

"Modern medicine tends to assume cancers and tumours in humans are diseases caused by modern lifestyles and environments," said Edward Odes of the University of Witwatersrand, in remarks quoted by New Scientist.

He said finds like this show that human cancer occurred long before modern societies.

It's not known if the cancerous bone belonged to an adult or child. But modern osteosarcoma is known to be most common in children and young adults. It typically occurs in fast-growing bones near the knee. Osteosarcoma was the kind of cancer that killed Marathon of Hope runner Terry Fox.

High-resolution 3D imaging

The discovery of the malignancy in the foot bone was made possible because of advances in high-resolution 3D imaging methods.

The finding was published online Thursday in the South African Journal of Science.

In the same journal, the same team of scientists also reported a groundbreaking finding of an even older fossil that had evidence of a tumour — but that one was benign.  

A 1.98-million-year-old vertebra of an Australopithecus sediba young male was found in a nearby site with evidence of a growth.

The previous oldest example of a benign hominin tumour was believed to date to a fossil rib from a Neanderthal who lived 120,000 years ago in what is now Croatia.

"Tumours of any kind are rare in archeological populations, and are all but unknown in the hominin record, highlighting the importance of this discovery," an abstract from the South African Journal of Science said.