Most cancers announce themselves with something obviously wrong — a limp, a bleed, weight falling off a dog that's still eating. Lymphoma usually doesn't. The typical presentation is a dog who is bouncing around the house exactly as normal, whose owner happens to scratch under the jaw one evening and finds two firm swellings the size of grapes that weren't there last month.

They don't hurt. The dog doesn't react. That combination — enlarged, firm, non-painful lymph nodes in a dog who seems well — is the single most recognisable signature of canine lymphoma, and it's the reason the disease is so often found by accident during a routine vaccination appointment.

What Lymphoma Actually Is

Lymphoma is a cancer of lymphocytes, the white blood cells that run the immune system. Because lymphocytes live everywhere — lymph nodes, spleen, liver, bone marrow, gut wall, skin — lymphoma can start almost anywhere in the body. That's what makes it different from a tumour that grows as a single mass in one organ.

Veterinarians classify it by where it shows up. Multicentric lymphoma, which affects the peripheral lymph nodes, accounts for roughly 80–85% of cases and is what most people mean by "lymphoma." The less common forms are:

It's a common diagnosis. Lymphoma is consistently listed among the most frequently diagnosed canine cancers, and unlike many of them it responds well to treatment — which is why it's one of the few cancer conversations where the vet's tone is often more optimistic than owners expect.

Which Dogs Get It

Median age at diagnosis sits around six to nine years, though lymphoma turns up in young dogs too. The Golden Retriever is the most consistently over-represented breed worldwide, with B-cell and T-cell forms occurring in roughly equal numbers. Boxers, Bullmastiffs, Rottweilers, German Shepherds, Basset Hounds, Beagles, Bulldogs, Airedales, Chow Chows, Poodles, Saint Bernards and Scottish Terriers all appear repeatedly in incidence studies.

Interestingly, breed risk isn't fixed across borders. A European canine lymphoma network study found that breed-associated risk differs meaningfully between countries, which suggests regional gene pools and possibly environmental factors are both at work. In practice, breed tells you to be attentive, not to expect the worst.

The Warning Signs

Learn where the peripheral nodes sit — you can check them in fifteen seconds during a normal cuddle:

Normal nodes are small and hard to feel at all. Lymphoma nodes are enlarged, firm, rubbery, freely movable and painless — often several at once, symmetrically. An abscess or an infected tooth can swell one node and make it hot and sore; several cool, painless nodes enlarging together is a different problem.

Other signs, when they appear, include lethargy, appetite loss, weight loss, increased thirst and urination (a clue to high blood calcium), swelling of the face or legs, and difficulty breathing. Vets divide patients into substage a — feeling well, eating normally — and substage b — clinically unwell at diagnosis. Substage b consistently predicts a worse outcome, which is a concrete argument for finding the nodes before the dog feels ill.

How It's Diagnosed

Diagnosis usually starts with a fine needle aspirate of an enlarged node: a quick, needle-only sample that in most cases identifies lymphoma on cytology alone, with no sedation required. Where cytology is ambiguous, a surgical biopsy of a whole node gives the pathologist architecture as well as cells.

The step that changes the conversation is immunophenotyping — determining whether the cancer arises from B-lymphocytes or T-lymphocytes. This is done by flow cytometry on a needle sample, by immunohistochemistry on biopsy tissue, or by PARR (PCR for antigen receptor rearrangements). Flow cytometry has become the common first-line choice and outperforms PARR at correctly assigning phenotype in dogs already known to have lymphoma.

Why it matters: B-cell lymphoma responds better and lasts longer. Dogs with B-cell disease on standard chemotherapy have reported median survival times around 300–365 days, while T-cell disease tends to sit at 235 days or less. Staging tests — bloodwork, blood calcium, chest X-rays, abdominal ultrasound and sometimes a bone marrow sample — fill in the rest of the picture before a protocol is chosen.

Treatment: What Chemotherapy Really Looks Like

The gold standard for multicentric lymphoma is a multi-drug protocol known as CHOP — cyclophosphamide, doxorubicin (hydroxydaunorubicin), vincristine (Oncovin) and prednisone. It's given as a series of mostly weekly outpatient visits over roughly 19–25 weeks.

Owners almost always arrive at this conversation picturing human chemotherapy, and that picture is wrong in an important way. Veterinary oncology deliberately prioritises quality of life over cure, using lower relative doses. Most dogs do not lose their coats, most feel well through treatment, and the common side effects — a few days of soft stool, mild nausea, temporary appetite dip — affect a minority and are usually manageable at home. Serious toxicity requiring hospitalisation is uncommon.

The results are genuinely good by cancer standards: roughly 80–95% of dogs achieve remission, with overall median survival times of about 10–12 months and around 20–25% still alive at two years. Dogs achieving complete remission do markedly better than those achieving only partial remission — one series reported median survivals of 683 days versus 241 days, against 119 days for dogs with no remission at all.

Remission is not cure. Around 95% of dogs eventually relapse, at which point rescue protocols come into play — re-inducing with CHOP if the first remission was durable, or switching to drugs such as lomustine, or to rabacfosadine (Tanovea), which received full FDA approval for canine lymphoma in July 2021 and produces response rates reported between roughly 50% and 100% depending on phenotype and how heavily pre-treated the dog is.

If Chemotherapy Isn't the Right Choice

Not every family can commit to a six-month schedule of clinic visits, and that's a legitimate decision rather than a failure. Prednisone alone is the usual alternative: it shrinks nodes quickly and most dogs feel dramatically better within days.

Be clear-eyed about what it buys, though. The Canine Lymphoma Steroid Only trial found a median overall survival of 50 days with prednisone alone, and only a 7% probability of surviving six months. There's a second catch worth knowing before you start: steroids given first can induce resistance to chemotherapy drugs afterwards. If full treatment is even a possibility, ask your vet before the first prednisone tablet is given, not after.

What to Take Away

Lymphoma is common, it moves quickly if untreated — weeks to a couple of months — and it is one of the most responsive cancers in veterinary medicine. Nearly everything that determines how the story goes is decided in the first two weeks: how fast the nodes were noticed, whether an aspirate was done promptly, whether phenotyping guided the plan, and whether steroids were started before the options were weighed.

So make node-checking part of the routine. Under the jaw, in front of the shoulders, behind the knees — a few seconds while your dog is already sprawled across your lap. If you find something firm and painless on both sides, don't wait to see whether it goes down. Book the appointment that week.