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Feline Small Cell Lymphoma

feline free internal medicine oncology

There’s almost no mistaking these cats when they come to your clinic.  Skinny with sometimes profound weight loss over several months, reports of worsening diarrhea and vomiting, and labwork not giving a lot of obvious clues or direction.  If that cat is entering their senior years, this is almost a slam dunk for small cell lymphoma to be very high on your differential list.  

This is an extremely common chronic disease in typically older cats and one that you will encounter with regularity in clinical practice.  The good news is that it is a highly manageable cancer that often carries good long-term outcomes!  We will be reviewing the clinical course and presentation of these cats, diagnostic work-up, and treatment recommendations which are nearly all easily achievable in general practice.


  • Documented or owner-reported weight loss, typically over many months to even years
  • May have a strong appetite despite losing weight although appetite may be decreased
  • Other signs such as vomiting, diarrhea, and nausea/food aversions may be reported
  • Examination findings – often thin body condition with muscle wasting, may palpate ropey or thick intestines and/or enlarged abdominal lymph nodes


  • CBC – may be within normal limits; mild to moderate anemia, neutrophilia, and/or lymphocytosis may be observed in some cases
  • Chemistry – often within normal limits unless concurrent disease is present; want to rule out renal disease and diabetes as differentials
  • TT4 – within normal limits unless concurrent disease is present; want to rule out hyperthyroidism as differential


  • If labwork is overall unremarkable with this history, abdominal ultrasound is next diagnostic step.  I would personally skip radiographs entirely at this point in favor of AUS.
  • GI tract typically displays thickened intestines, whether diffuse or segmental, with muscularis thickening being most striking finding
  • Mild to moderate abdominal lymphandenopathy often present
  • Occasionally can see other changes in liver and spleen to suggest additional disease spread

At this point, you know you are likely dealing with either inflammatory bowel disease or small cell gastrointestinal lymphoma in your feline patient.  How can you differentiate between the two conditions to help guide treatment and prognosis for the owner?

Fine needle aspirate?
  • May be able to collect a sample from enlarged node or more profound areas of GI thickening
  • Often will not be diagnostic on initial pathologist review as both conditions will typically show an overabundance of small “normal appearing’ lymphocytes
  • Expect to need additional testing such as PARR on the sample to truly differentiate the diseases (so build that into any financial estimates

Surgical biopsy?
  • Likely to provide the “best” samples if the owner is willing to go for it as full-thickness biopsies can be taken from different parts of the affected GI tract
  • Can reach and sample mid to distal jejunum which is not possible with endoscopy
  • Can also sample other non-GI abnormalities (ie lymph nodes, liver, etc.)
  • Procedural risk is quite low but cost and owner concern for healing and anesthesia may be barriers

Endoscopic biopsy?
  • Less invasive with no surgical healing time
  • Limitation in the depth of tissue sample that can be obtained (ie not full-thickness) so may miss the lesion that is present
  • Limitation in reaching all parts of affected GI tract and unable to sample any lesions outside the gastric and intestinal walls
  • Often requires referral to be completed with associated cost and wait-time

There will of course be owners that will refuse to complete any of these diagnostic tests in which case you will need to make your best efforts toward treatment without this confirmed diagnosis.  The good news is that IBD and small cell lymphoma have very similar treatment options so there is plenty you can do!   I also get a lot of questions about completing a “GI Panel” on these cats to look for changes in cobalamin and folate.  This is of course what you probably should do on all of these cases to be complete but these are not cheap tests to run and a high proportion of them will invariably tell you the cat is cobalamin deficient.  I personally am comfortable assuming this deficiency is present and supplementing vitamin B12 as outlined below even without proof through testing.


  • Treatment for cats with CONFIRMED small cell lymphoma
    • Prednisolone – 1-2 mg/kg/d.  Typically this comes out to about 5 mg per cat per day.  Consider liquid or transdermal formulations to improve compliance.
    • Chlorambucil
      • Every other day dosing at around 2 mg per dose is possible but is more burdensome for owners
      • Pulse dosing makes it much easier!  20 mg/m2 given once every 2 weeks.
      • Recommend compounding with a reputable pharmacy to keep costs low
    • Vitamin B12
      • 250 ucg (0.25 mL) administered SQ weekly for four weeks then every other week for two doses
      • Some cats benefit from monthly administration but most will not need it if responding well to treatment
    • Supportive care as needed – mirtazapine, Cerenia, Elura, metronidazole, probiotics, etc.
  • Treatment for cats with POSSIBLE/SUSPECTED small cell lymphoma (vs IBD)
    • Introduce hypoallergenic or limited ingredient diet appropriate for IBD control
    • Start prednisolone as instructed above
    • I personally recommend holding on chlorambucil for approximately 8 weeks to see if this regimen alone is enough to control cat’s disease
    • If continued clinical signs are observed, can discuss introducing chlorambucil at that time


  • Examination, weight check, and CBC 1 month after starting therapy
  • Examination, weight check, CBC/chemistry, and abdominal ultrasound 2 months after starting therapy
    • If patient clinically improving with corresponding improved AUS, recommend exams and labwork every 2-3 months
    • Look for trends in weight or owner-reported relapse in clinical signs.  I usually only recheck an AUS when I am suspicious of relapse (not at every recheck).
    • CBC – look for neutropenia as sign of immunosuppression from chemotherapy as dose may need to be lowered.  Look for anemia as this is common in this disease.
    • Chemistry – monitor glucose levels as pred-induced diabetes can occur.  I’ve had luck in switching these patients to budesonide and having the diabetes enter remission.
  • If patient not improving/not entering remission, may need to consider rescue or alternative chemotherapy such as cyclophosphamide or CCNU (or even radiation therapy)
    • Majority (>85%) of cats should do very well and enter remission on above protocol!
    • For the few that don’t, they can be challenging to control and may need oncologist or internist to manage rescue options


  • After cat has been in clinical remission or had a documented strong response for a year, I will recheck an ultrasound to confirm this
  • Can then discuss weaning/tapering of therapies
    • Will first discontinue chlorambucil and recheck weight in 1 month
    • If doing well and no relapse is suspected, will then taper prednisolone to every other day for 1 month then discontinue entirely
    • Recheck examination and weight 1 month after stopping prednisolone
  • Recommend quarterly examinations and weight checks on these patients to try to catch relapse early, sooner if any concerns are noted at home by the owner
  • If disease relapse occurs, you can often reintroduce the same therapies and expect another response
  • Prognosis tends to be good!
    • Reported averages of 1-2 year survival times but this seems, if anything, low to me
    • Will consistently have cats living >2 years with this disease with not all of that time involving active therapy and treatment
    • Quality of life on treatment and side effects from therapy tends to be very acceptable to owners

Small cell lymphoma in cats is exceedingly common and, for most of the cases you will encounter, exceedingly simple and rewarding in their management.  The improvement in these cats with treatment can be profound and accomplished in even just a short time on therapy.  This is absolutely one of the diseases in which the pressure to practice “gold standard” medicine and complete every diagnostic test in the book should be lifted away to make it within the reach of owners.  Please don’t hesitate to reach out with any questions about case management or the information outlined in this summary!


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 About the Author: Kathleen Tidd, DVM, DACVIM (Oncology)

Dr. Kathleen Tidd is a Pennsylvania native who completed her dual degree undergraduate work in Toxicology and Animal Biosciences at Pennsylvania State University before receiving her veterinary degree at North Carolina State University. She completed a year-long rotating internship in a busy Pittsburgh private practice which solidified her love of oncology. After becoming boarded in medical oncology through a residency at the University of Pennsylvania she accepted and currently holds a position with The Oncology Service in Virginia. She currently serves as program director of the oncology residency program at the hospital.


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