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>  Would it be possible for multiple types of "cancer" cells (or at least host foreign animal cells) to work in unison to create new structures? 

Normal cancer, inasmuch as there is such a thing, doesn't really seem to work like that... cancer cells are fundamentally broken things, because of the wide range of safeguards that healthy cells have to prevent them becoming cancerous. They carry on doing the things they used to do, to the best of their ability given their damaged state.

> For example, extending a cardio vascular system, 

Angiogenesis is very much a thing in many kinds of tumour, but it isn't the cancer cells themselves forming the blood vessels. Instead they make use of existing signalling mechanisms to induce healthy tissue to form new blood vessels to feed the tumour.

> or nervous system through out the tumor

Whilst blood vessel (re)generation is a common trick, regrowing nerves (and especially regrowing nerves _quickly_) is rather more limited. It doesn't seem totally beyond the realms of possibility, but it does seem dubious, if you were expecting to have complex signalling through the tumour.

> or, at the most far fetched side of things, a new appendage, like a cancerous "ear" formation

Stem cell cancers can produce differentiated tissue, but the structures seem to be fairly simple (see above, cancer cells are broken) and messy things.

In a species with the ability to regerate complex structures it might be possible for a cancer to hijack regeneration mechanisms in the same way that more conventional mammalian cancers can hijack angiogenesis. This wouldn't be an effect that could cross species though; the capability would have to be present in the "host" species infected by your transmissible cancer, rather than being something the cancer could bring itself.

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As a potentially interesting aside, stem cells can be quite hazardous in themselves... there's at least one documented case of someone undergoing experimental stem cell therapy ending up with healthy snot-producing cells developing _in their spine_. Removing proliferating but healthy stem cells is much harder than dealing with cancer as the usual mechanisms of cancer treatment are much less effective on healthy cells (obviously).

[Autograft-derived spinal cord mass following olfactory mucosal cell transplantation in a spinal cord injury patient](https://thejns.org/spine/view/journals/j-neurosurg-spine/21/4/article-p618.xml)