Mom is 91, chf, vascular dementia post stroke, post broken hip repair, pacemaker a month ago. 15/15 on last mini mental but can't reason her way out of a paper bag. Do we find a pulmonologist to figure out if she needs a chest tap? She is very out of breath if she rises from wheel chair to use the bathroom. Won't / can't participate in activities. Leave well enough alone?
...and, well, probably no use beating around the bush here, Ba8alou, the atypical cells and the fact that it's not going away with antibiotics suggests cancerous tumor, primary or metastatic in that lung. The decision to put in the pacemaker probably reflects a reasonably good quality of life, and you may have more decisions to make. It may be valid to limit investigations for cancer if she could not withstand treatment for it ,but every case is different and there are a lot of things to consider. It is usually very possible to keep someone comfortable and ease their breathing, even repeating the pleural (chest) tap as needed will bring some relief most likely. Ideally, if you can handle it emotionally, let the staff know you are ready, bring that box of Kleenex and ask the doc to give you the straight story.
Pleural Effusion is a build-up of fluid in the pleural space surrounding the outside of the lungs. It is usually caused by other pre-existing conditions; bacterial pneumonia, cancer, PE, left ventricular failure, etc.
healthline/health/pneumonia#Overview1
Pneumonia can be caused by a fungus, virus or bacteria, or other agents
Pneumonia shots innoculate against only one kind of pneumonia.
Signs of pneumonia are congestion, respiratory difficulty and greenish sputum. If she has those, a trip to the ER is indicated.
I'm not a medical person and could only give you a definition of pleural effusion based on one of the medical sites.
How long has she been out of breath? Is she getting any PT, or any exercise? Is she on oxygen?
Given your concerns, I think I'd take her to the ER; even if she doesn't have a pulmonary or cardiologic emergency, you'll at least know that you avoided something more seriuos, then can see follow-up doctors based on the ER diagnosis.