Hi,
It is difficult to comment on the case without seeing the biopsy report. If the results were truly inconclusive and the cat isn't doing very well (not eating well, seems painful etc.), then further testing may be necessary. If you aren't getting the satisfaction that you need from your current veterinarian, then pursue a second opinion. You may want to inquire about a referral to a specialist if there is one in your area.

Good luck,
drphilvegasvet