The genetics-environment question is key to understanding cancer.
AUC professor Salima Ikram, a member of the team that studied the mummy in Portugal for two years, said Sunday the mummy was of a man who died in his forties.
She said this was the second oldest known case of prostate cancer.
"Living conditions in ancient times were very different; there were no pollutants or modified foods, which leads us to believe that the disease is not necessarily only linked to industrial factors," she said.
A statement from AUC says the oldest known case came from a 2,700 year-old skeleton of a king in Russia.