A cancer needs a good blood supply to provide itself 
  with food and oxygen and to remove waste products. When
  it has reached 1 to 2mm across, a tumour needs to grow
  its own blood vessels in order to continue to get
  bigger.

  Some cancer cells make a protein called vascular
  endothelial growth factor (VEGF). The VEGF protein
  attaches to receptors on cells that line the walls of
  blood vessels within the tumour. The cells are called
  endothelial cells. *This triggers the blood vessels to
  grow so the cancer can then grow.*

OK, what about this trial...atezzolblablblah.. What's it do?

  Programmed cell death protein 1 is a cell surface
  receptor that plays an important role in down-
  regulating the immune system and promoting self
  tolerance by suppressing T cell inflammatory activity. 
  PD-1 is an immune checkpoint and guards against
  autoimmunity through a dual mechanism of promoting
  programmed cell death in   T-cells in lymph nodes while
  simultaneously reducing cell death in regulatory T
  cells.

  ...

  PD-L1, the ligand for PD1, is highly expressed in
  several cancers *and hence the role of PD1 in cancer
  immune evasion is well established*.

This thing isn't just some dumb pathogen floating around that just DoSes your body. It's digging tunnels and cutting phone lines. It has strategy.

Cancer cells simply lack the trigger to stop growing.

See also epithelial to mesenchymal (ETM) transition, in which cells lose their anchors and become an entirely different kind of cell so that it can better infiltrate other parts of the body.

It's pernicious and highly specialized because that's why it survives. And that's why everyone will die of cancer if something else doesn't kill you first.

EDIT: OK I've done some reading about cancer and evolution. Clearly there is an evolutionary process happening inside each person's body that "selects" for cancers that are good at their "job". However even the most successful of those have no hope of passing beyond their host unless they also mutate a transmission mechanism for themselves, which happens much less often (but the Internet tells me it has been known to happen in dogs).

Generally, infectious cancer is a result from a population that either regularly has open wound contact, and or is very closely related genetically.

Given enough time cancer can even start to survive on it's own: https://en.wikipedia.org/wiki/HeLa It's actually become somewhat difficult to avoid cross contaminating samples with this cell line.

Oncoviruses are another transmission vector. HPV, or human papillomavirus, is a virus that causes warts (of all kinds) in humans, and also causes several kinds of cancer, including cervical and esophageal cancers.

A third way would be a pretty rare thing in humans, but is thought to be behind some of the canine cancers you mentioned: direct transplantation of cells. The tasmanian devil is on the edge of extinction thanks to a facial cancer they get from each other through this mechanism.

esp. in combination with studies r intermittent fasts/food in general. Neven Orhel's (fiction) books are also in the line with intermittent extremes / how healthy cells can cope with them and cancer cells can not, which is well in-line with the finish saying(was something like "if sauna doesnt cure you no doctor will" - pls correct me here)

The cancers that haven't mutated to emit VEGF don't survive to grow and kill you.

It's natural selection, not intelligence.

+1, Fuck cancer.

Your comment made me cry.

"Squeeze her hand for a stranger."

OP, I will keep your wife in my thoughts.

I'm crying, my Mom passed away almost 3 years ago, but that sentence got me. Godspeed to the Scientists and best of luck OP's wife.