This is a tough question to answer (and probably better for Sarah to answer!): perhaps we have become better at diagnosing cancer than we were before. However, it is possible that because we are exposed to a wide range of environmental contaminants, radiation, etc, this could increase the likelihood of cancer, but I have not seen any statistics.
Cancer isn’t more common now. It’s always been with us.
Cancer is an ancient disease. They have found the fossilized remains of ancient humans with bone cancers. The Egyptian mummies have been found with breast tumors. And the earliest writings (from about 1600 BC) mentions “there is no treatment”.
The origin of the word cancer is credited to the Greek physician Hippocrates (460-370 B.C.), considered the “Father of Medicine.” Hippocrates used the terms carcinos and carcinoma to describe non-ulcer forming and ulcer-forming tumors. In Greek these words refer to a crab. This is because when he dissected people with tumours, the tumours looked like a crab living in the person’s body because of the round ‘body’ and the arms that projected out from it (arms are big blood vessels that the tumour feeds from).
There isn’t ‘more cancer’ now. The illusion is caused from several factors: more people are now on the planet and people live longer, older people tend to get more cancer than younger people and advances in medical treatment now means more and more people are surviving. We also have more diagnoses too just as Tom said.