It was described in an Egyptian manuscript (see featured image) from 1600 BC. There were also references from Hippocrates, who referred to them as “carcinos”, the Greek word for crab, which explains why the astrological sign for cancer is a crab.
Though the first occurrence was reported out of ancient Egypt (an advanced civilization, so it obviously must have gone unreported in less advanced civilizations), it looks like it was very rare until modern times and, presumably, an increase in the manufacturing and synthetic things of modern times:
Some of the earliest evidence of cancer is found among fossilized bone tumors in human mummies in ancient Egypt, and references to the same has been found in ancient manuscripts. Bony skull destruction as seen in cancer of the head and neck has been found, too.
It also says that it is quite a bit older than what we saw above and references a cauterization processes by a terrifying instrument called a “fire drill”:
Although the word cancer was not used, the oldest description of the disease is from Egypt and dates back to about 3000 BC. It is called the Edwin Smith Papyrus and is a copy of part of an ancient Egyptian textbook on trauma surgery. It describes 8 cases of tumors or ulcers of the breast that were treated by cauterization with a tool called the fire drill. The description adds that there is not treatment for the condition.