Can cancer worsen Alzheimer's symptoms?

My mom is in late moderate stage Alzheimer's with recurring colon cancer. We stopped chemo on November 4th after only two months of treatment because it seemed to worsen the Alzheimer's. The past week she has suddenly declined rapidly, hallucinating more and more and being agitated more easily and then very loving apologizing for it. We stopped Aricept for a week and that didn't help so we put her back on but only in the mornings. This all was done with doctor suggestions. Could her cancer and Alzheimer's combined be causing her to decline so fast? What would signs be that her cancer could be spreading and causing the decline? I will be calling the cancer doctor and neurologist tomorrow, but your opinion too would be greatly appreciated and I understand it would ONLY be an opinion from my describing of this and you not knowing her personally. Thank you.