Since a tumor isn’t conscious, there’s no deprivation. And since animals don’t have a future like ours, they don’t qualify. The argument rides on a fetus having a future like ours, an ongoing life in pursuit and toward enjoyment of hobbies, interests, relationships, thoughts, experiences, etc.
Note that this doesn’t imply it’s permissible to kill animals for mere enjoyment or with no justification — it’s simply an argument for establishing that it’s seriously morally wrong to kill an innocent being that has a future like ours. We could add to this a case for the immorality of killing animals in certain ways based on their capacity to feel pain. This is not human-life-specific, either — it could turn out that we detect alien life whose futures are like ours. These would qualify, too.
You could try to equate “a future like ours” with the concept personhood, but that’s an unncessary move. All you need is the “future like ours” concept for Marquis’ argument to work.