system
Given the following post, respond as if you're commenting on Reddit:
human
How common were various forms of cancer before the 20th century?
gpt
Very hard to assess, because of one really big problem: Diagnosis sucked.  If you have someone come in coughing up blood and losing weight in the early 1800s, what's your diagnosis? Hint: It ain't lung cancer.  Tuberculosis was so rampant, any lung disease with related symptoms was classified as consumption (which was killing something like one in four people in Europe at the time).  Post mortem autopsies weren't routine, and common cancer types like leukemia weren't even discovered until the mid 1800s.  X-rays are a recent invention, so you couldn't see most tumors without invasive surgery. 

All that said, cancer rates go up with age.  The rate in of death by cancer for a 20 year old is .06 people per thousand per year.  For an 85+ year old, it's 26 people per year per thousand (43 times higher risk). So it's probably safe to say that people in the past almost certainly got less cancer than we get today, because they weren't living as long.