Depending on what makes it a "cancerous tumor", it might be possible to make it develop into something like that.
Generally speaking, by the time you see a cancer you have cells with genetic material that is severely broken. However, it is not always so and in some cases the malignant phenotype can be reversed (I think we are mostly about talking experimental settings, though). That is, in theory, depending on what is broken & how badly it is broken, in some edge cases some cells can be encouraged to behave like a malignancy or to revert to acting like a normal cell.
In such a scenario, I could imagine that after some manipulation we could also reprogram this cell into an embryonic path development instead of a terminal somatic differentiation path.
But more to the point, a biopsy specimen from a human is also going to be human but it won't be a huma being. Nevertheless, we should be able to have some such clinical specimens develop into human beings if we use the proper techniques (we call that cloning).