A Large Back Cyst That Keeps Refilling
by A reader
We can't tell whether it's cancer without testing, and nobody can tell just by the color of the fluid. Yellow fluid is common in cysts and in seromas (pockets of fluid under the skin). A dark, syrupy color often means old blood inside the lump, which can happen after repeated draining. Most fluid-filled lumps are benign, but a few tumors can form fluid-filled spaces, so a lump this size that keeps coming back should be checked properly.
Ask your vet whether the fluid has been sent to the lab. If not, the next steps are usually to examine the fluid and cells under a microscope (cytology) and, if that isn't clear, to take a biopsy or remove the whole lump and send it to a pathologist. An ultrasound can show whether it's a simple sac or has solid parts.
Repeated draining also carries a risk of infection, and draining alone rarely cures a cyst that keeps refilling. Removing the whole thing, including its lining, is usually what stops it and also gives you a definite answer. Have it seen soon if it grows quickly, becomes hot or painful, opens up, or your dog seems unwell.
See cysts on dogs and lumps and bumps on dogs.
This is general information, not a diagnosis. Please follow your own vet's advice.
