Are Polyps Usually Cancerous?

I was told I have two kidney stones a month ago that are 5cm and 2 cm in size in my left kidney. I also had prostatitis symptoms of "that golf ball feeling" and a 4 of 8 score on the dipstick for blood. That was pre-antibiotics and 3 days later I had no blood, again pre-antibiotics. I've had two different DRE's from two different URos and both were ok. Had BPH for 20 years (58) and been on Hytrin 10 mg QD during that time. Three weeks ago, I had a CAT, sono and KUN, I had 17 days of 500 mg Cipro and felt 95 percent better after two days and 100 percent after 17 days (two weeks ago) This Monday I get a cystoscope and started Cipro pre-procedure 500mg BID tonight per doctor's instructions. I started having a tingling in my urethra 24 hours ago. My uro wants the cysto to rule out bladder polyps. If I have a polyp are they usually cancerous? Would prefer answer from a Urologist.