Transitional cell carcinoma (also called urothelial carcinoma) is a cancer of the cells lining the urinary bladder, most commonly arising at the trigone — the area where the ureters enter the bladder and the urethra exits. This location means the tumour frequently obstructs urine flow as it grows. The cancer develops from the transitional epithelium, a specialised cell layer designed to stretch and contract as the bladder fills and empties. A specific genetic mutation called BRAF V595E is found in approximately 85% of cases and can be detected through a non-invasive urine test, aiding early diagnosis. Scottish Terriers are at dramatically elevated risk. The trigone location typically precludes complete surgical removal, so treatment usually relies on a combination of non-steroidal anti-inflammatory drugs (which have direct anti-tumour activity in this cancer) and chemotherapy to control disease progression.