system
Given the following post, respond as if you're commenting on Reddit:
human
[Alien/Warhammer 40K] If a chestburster somehow managed to survive inside a space marine and grow into a full xenomorph, how fucked would that particular planet be?

Assume for this question that the Xeno somehow manages to get out, killing the space marine as unlikely as that is. How powerful would the resulting Xeno be with space marine DNA?
gpt
Actually, with all of the redundant organs, it's unlikely the hatching xenomorph even would kill the space marine. At the very least, it's unlikely the space marine would die before he killed the larval stage of the xenomorph. But even assuming it happened? 

Space Marines face their own brand of "xenomorph" all the time - genestealers. And they've absorbed Space Marine DNA in the past. The result are the Tyrant Guard - big, strong, immune-to-pain, almost-unkillable versions of normal genestealers.

So, the planet might be fucked. But on the other hand - which planet? Remember, the Empire is not our universe, it's much more capable and hardened in many respects, and, importantly, the Empire has lots of experience dealing with foothold invasions of rapidly-reproducing aliens. So yeah, if it's an agri-planet or a barbarian "lost" world? Sure, probably bad. Some half-forgotten burned-out hive world? Yeah, that's going to get ugly, quick. But some world like Mars, or Macragge? Nah, probably not, they have ample resources to draw on to fight it. Fenris? Pity the *xenomorph*, not the planet's population.