A 65-year-old patient complains of frequent painful urination, moderate weight loss observed over the last 3-4 months, and massive microhematuria with excretion of shapeless blood clots. According to the patient's medical history, macrohematuria first appeared 3 months ago with no apparent cause and was not accompanied by pain and dysuria back then, a few days later the bleeding stopped on its own. What is the most likely diagnosis in this case?