Is cancer the effect of the stopping of cellular changes in interphase?

That's a really bad question that you have to answer. If certain mitogens (growth factors) are not present during interphase, a cell may go into what is known as G0, or suspended interphase. It will not undergo mitosis indefinitely in this phase. If it does receive the right signals, gene regulatory proteins will be activated and the cell will prepare for S phase. I'd rather not go into the details of that, but... yeah, the question sucks. Problems with the G1/S checkpoint can cause cancer, but I don't think that's the answer they're looking for.