A pre-malignant cell is, in simple terms, one "step" before the cell becomes cancerous. Pre-malignant cells some some of the hallmarks you find in cancer, but not all of them. They have the potential to develop into cancer, and often do (unless of course, you kill or remove those cells).
I'm not exactly sure what you're referencing with "Positive A cells". Without more information, I can only guess. My best guess is that your wife was diagnosed with pancreatic cancer, and the doctors are talking about alpha cells (which are endocrine cells located in the pancreas) that are positive in some respect (such as showing certain signs of cancer).
Next time a doctor starts using a ton of technical jargon, ask them what it means, and ask them to explain it in terms that you can understand. Pretty much all doctors can and will do this, they just don't think to do it unless asked. If they don't answer your questions satisfactorily, or you still don't understand the answer, don't give up--keep asking until you get a straight answer that you understand. It's your wife's right as a patient to informed consent, so if she asks them a question about her treatment, tests, et cetera, they basically HAVE to answer it.
Hope this helps, and I wish you and your wife the best.