Is it possible to deliberately get cancer? Maybe injecting a malignant tumor? I'm asking this just out of curiosity.
A decent share of radiation will do the trick for you, as both Hiroshima and Nagasaki, but also physicists experimenting with the newly found radiation have shown.
There even is a unit (sievert) which measures how cancerous a dose of radiation is. One sievert is equivalent to a 5,5% chance of cancer.