[Nextgrid]

It has the same purpose as us, just that while our "world" is the Earth (or whatever planet our species will conquer before extinction), its "world" is merely the human body it inhabits.

The death of a cancer's host body is like our equivalent of our star dying, and I guess our equivalent of interplanetary colonization would be a hypothetical cancer's ability to jump between hosts.

[dredmorbius]

Neither humans nor any other known life-forms can meaningfully influence stellar evolution regards either the fate or timing of the Sun's end.

Cancer can and does bring about the death of its host.

(One might argue that both humans and other life forms have the potential and/or demonstrated capability to transform their own ecosystem beyond its viability to continue to sustain and support them, with both the present anthropogenic greenhouse-gas-based global warming and the Great Oxygenation Event and subsequent Snowball Earth serving as examples.)

That said, I understand your analogy.

There are virally- and clonally-transmitted or otherwise contagious cancers:

<https://en.wikipedia.org/wiki/Clonally_transmissible_cancer>

(These are rare and seldom found in humans.)