Let’s say, for instance, someone with lung cancer coughs, and a few cancer cells are present in the aerosol, and is breathed in. Or, if someone has a cut, and lives with a family member who has cancer, and cancer cells end up in the cut.
Cancer cells are a bit like HIV in that they evade the immune system by releasing some chemical to trick it. Hence why in an infamous unethical experiment after the war, people injected with another person’s cancer developed cancer. So even if it is another person’s cancer cells, the cancer will metastasize in the body.
This would make cancer the most overlooked infectious pandemic in all of human history.
Humans reject other tissue from other humans. It’s seen as foreign. It’s why transplant recipients have to take drugs to suppress their immune system.
Also here is what cancer is:
It’s human cells that have mutated that now grow incorrectly (too fast or erratic). Or Human cells growing in the wrong place in the body. Or a combination of the two.
They mutate for a number of reasons but they are that person’s cells. Have their dna.
There are many factors that can make the wrong cell type grow in a different area. Usually chronic prolonged damage causes this.
But That’s why the body can’t get rid of them. They are part of you. They aren’t foreign.
This is also why they aren’t contagious. Cancer is a product of the individual’s cells not growing how they should.
Not someone else’s cells taking over. Not a virus. Although some viruses and bacteria infections increase the risk of cancer developing. Like hpv. And h.pylori.