If it doesnt stop him peeing or upset him, leave it. Some vets will tie a piece of cotton thread around the base and it drops off. You could ask about Feldene, which stops further growth in some cases.
"
Feldene (generic name
piroxicam) is a nonsteroidal anti-inflammatory drug (NSAID) and COX-2 inhibitor that has shown promise in treating squamous cell carcinoma (SCC) in horses, particularly when conventional methods like surgery are not possible or when the cancer has metastasized. While not a primary cure, it is used to manage and slow the progression of the disease."
We use this method on Bibble. Last year when he let down for vets under a light GA, they could see not further growths, which was encouraging.