Similar: Why isn't cancer contagious? (Or IS it?)

Ok second cancer one–Now that i figured out what it is, why can’t cancer be contagious? Or is it?

If the cells just keep multiplying, if someone got injected somehow with someone else’s cancerous cells, would they not get cancer? Wouldn’t those alien cells keep multiplying?

The immune system might kill it, but is that a certainty?

And if injecting say, Henrietta Lacks’ cells into someone would give them cancer, what if a testube broke and the cancerous cells went into the air and people breathed them in?

Tasmanian Devils’ Existence Threatened By Rapidly Spreading Cancer

The simple answer is no because our genetic code produces a group of molecules on host cells called the major histocompatibility complex which allows ones immune system to differentiate host cells from non-host cells. Anything non-host can then be targeted by the immune system and killed off.

By and large, yes, it’s a certainty. There are certain factors that may allow someone else’s cancer cells to grow in a different host (transplant patients on lifelong immunosuppressants would be my best guess, or those immunocompromised due to loss of T-Cells), but those are relatively speaking fairly rare occurrences.

Airborne cancerous cells, assuming they could survive long enough, would still need a vector to get past the body’s natural barriers to entry–ie past the mucous membranes, layers of keratinized epithelium, etc. Bacteria and viruses have evolved such methods. Human cells haven’t.

But, if you insert cancerous cells directly into the body, some cancers are transmissible:

There’s also a form of canine venereal cancer that is transmissible:

I’ve read about this before, I think someone got cancer from a kidney transplant. It is probable that they were on immunosuppressants which would allow for the cancer to spread into the new host more easily.

Isn’t cervical cancer generally associated with the human papillomavirus (HPV)?

This recent column by Cecil may be of interest: Can dogs get venereal disease?

Yes, though the transmitting host may never get cancer even if the recipient does, and not all HPV strains have the potential for causing cervical cancer.

…which has always made me wonder how many other cancers and chronic conditions might be caused by viruses of which we are simply unaware.

Would cancer cells from one identical twin be able to take root in the other, for example during a transplant?