From what I understand, fatty tumors are not all that uncommon in dewlaps. Did the vet poke at it? Sometimes they can tell if it feels like fatty tissue or not. There are other possibilities, of course. Cancer, cyst, abscess, etc. They would feel differently and I would think the vet would want to do a biopsy if they thought it was suspicious.

Lipomas (fatty tumors) are not uncommon in rabbits, as mentioned above, and I read that many develop in the dewlap. If the lump hasn’t grown or changed in all this time, I would find that very reassuring. Plus your rabbit is not showing signs of illness or weight loss, which usually goes along with something more sinister, so I’m thinking everything is fine. I know it’s unsettling not knowing exactly what it is, but knowing that it is almost surely NOT serious is good! ☺

If you still have concerns, ask if a blood test would give any indicators if it’s not a benign lump. That would be less invasive.

Vet fees can get expensive!! It might be worth looking into insurance for your bun. This particular issue would be classed as pre-existing but insurance may save you down the track for anything else. VPI cover rabbits and it’s about $12 a month, I believe.

I wish pet insurance in Australia covered rabbits!!

If it’s “free-flowing” in there and “rubbery” when you gently press it with your finger-tips, it’s most likely a lipoma. Malignant tumors tend to invade nearby tissue. Malignant tumors are often uneven in shape whereas lipomas are rounded because they have a capsule of connective tissue walling them off.

Putting her on a diet won’t shrink the lump. Weight-gain might make it bigger though and it’s always best to feed a healthy diet, but the cause of a lipoma is not the diet.