An 82 year old female with end-stage renal failure presented with bilateral pleural effusions following a missed haemodialysis session. Her stay was complicated by hospital-acquired pneumonia. A pleural tap was performed and fluid was submitted for cytological analysis. Representative Papanicolaou-stained smears are shown (Figures 1-3). Diff-Quik-stained smears were largely acellular; an attempt to produce a cell block for further investigations was unsuccessful.
What is the most likely diagnosis?