The most likely cause of fluctuating jaundice in a middle-aged or elderly man is -

Periampullary cancer is a cancer that forms near the ampulla of Vater, an enlargement of the ducts from the liver and pancreas where they join and enter the small intestine.It consists of: . ampullary tumour from ampulla of Vater 2. cancer of lower common bile duct 3. duodenal cancer adjacent to ampulla 4. carcinoma head of pancreas It presents with painless jaundice which may have waxing and waning nature because at times the sloughing of the tumor tissue relieves the obstruction paially. Ref Davidson edition23rd pg802