Yes, this could well be cancer if it also contains solid component only! Renal cysts are very common an incidental finding in routine imaging studies; but most are benign cysts. However, renal cell carcinoma could be associated with cysts but some solid component remains there especially in elder people and cause hematuria, infections and pain. Only a simple fine needle biopsy relieves tension in doubtful cases; it is done under USG/CT guidance and is a very common safe procedure; sometimes aspirates whole fhid component thus curing the disease also! Therefore not to worry much but see a urologist for discussion and to determine the plan of management. regards,