Hello, I am Dr Ola B and I am a licensed veterinarian. I am so sorry that Sheena isn't feeling well and that you had such a bad experience with the previous veterinarian. Honestly, even if your veterinarian was suspicious of cancer, he didn't handle this well.. The first thing that needs to be ruled is a lower urinary tract infection and/or the presence of bladder stones. Only when infection (or in cats, lower urinary tract disease) or bladder stones are ruled out as reasons for inappropriate urination, can cancer be suspected. If your veterinarian did a urinalysis, urine culture, abdominal x-ray and blood work and all of these test were inconclusive, then bladder cancer may need to be considered. Cancer that affects the bladder in cats and dogs is known as transitional cell carcinoma is unusual in that it affects the bladder wall and can only be detectable and tested via ultrasound.
Here is a little more information about how the etiology of this and how is diagnosed or ruled out:
Furthermore, if Sheena does have a urinary infection and your veterinarian did not complete proper testing, steroidal medication can make matters worse as steroids can suppress immune function. I do believe it may be best for your to get a second opinion on this if only to find a doctor that you feel have a better comfort level with...
hope this advice was helpful to you. Please let me know if you need clarification on anything or have other questions about this. Also, please do not forget to rate my answer which I hope you found to be "excellent." You may do this by clicking "rate our conversation" below (Your rating is the only means of compensation I receive for answering your question). Again, let me know if I can help you further:)