"Thymoma"
GULF COAST VETERINARY ONCOLOGY'S TUMOR TIDBITS
Volume 2, Number 5: April 2001
This Month's Feature: Thymoma
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Editor: Kevin A. Hahn, DVM, PhD, Diplomate American College of
Veterinary Internal Medicine (Specialty of Oncology) & Overall Nice
Guy; Gulf Coast Veterinary Oncologists, Houston, TX 77027,
drhahn@gulfcoastvetspec.com
_____________________________________________________________________
ANNOUNCEMENTS
Seeking - Full-time technician (RVT preferred) in Medical Oncology.
Available immediately. Monday-Friday, No Weekend or Overnight Duties.
Good pay/health and retirement benefits.
Seeking - Full-time Medical Oncology Fellow (1 year renewable
appointment) and Medical Oncology Resident (3 year nonrenewable
appointment). Available immediately.
Schedule an appointment with Dr. Hahn or call 713-693-1166 or fax
resume to 713-693-1167.
______________________________________________________________________
Tidbit Topic: THYMOMA
OVERVIEW: Originates from thymic epithelium and is infiltrated with
mature lymphocytes, Rare in dogs and cats, Occurs most commonly in
medium- and large-breed dogs, Dogs--mean age, 9 years, Cats--mean
age, 10 years.
SIGNS: Coughing, Tachypnea, Dyspnea, Swelling of the head, neck, or
front limbs (ie, anterior caval syndrome), Muscle weakness and
megaesophagus caused by myasthenia gravis. About 20-40% of animals
with thymoma are also diagnosed with nonthymic tumors, polymyositis,
and other autoimmune diseases.
DIFFERENTIAL DIAGNOSIS: Lymphoma, Branchial cyst, Ectopic thyroid
carcinoma, Chemodectoma.
DIAGNOSTIC FINDINGS: Lymphocytosis in a few patients, Thoracic
radiographs reveal a cranial mediastinal mass, pleural effusion, and
megaesophagus in some patients, Cytologic examination shows mature
lymphocytes and epithelial cells, Evaluate for myasthenia gravis if
the patient has signs of muscle weakness, dysphagia, or
regurgitation.
LOCAL TREATMENT OPTIONS: Surgical excision the treatment of choice.
Thymoma tends to be highly invasive and difficult to resect in dogs,
but less invasive and easier to remove in cats. Use an intercostal
approach for small masses and a sternotomy for large masses.
Radiotherapy of potential benefit by reducing the lymphoid component
of the mass.
CHEMOTHERAPY AND OTHER MEDICATIONS: Prednisone (20 mg/m2 q48h) and
cyclophosphamide (50-100 mg/m2 q48h) have been used in a very limited
number of patients. Two patients had a partial remission. Vincristine
has been used in a limited number of cats and dogs with partial
remission (5 pets) and complete remission (1 dog) observed.
Myasthenia gravis treated with prednisone and anticholinesterase drugs
until the tumor can be removed.
FOLLOW-UP: Thoracic radiography every 3 months to monitor for
recurrence, Cure possible if tumor is surgically respectable,
Prognosis is poor for patient with nonresectable thymoma.
BEST PROTOCOL AT GULF COAST: In pets with nonresectable disease we
use a combination of radiation (3 times per week for 6 weeks) and
weekly Vincristine therapy. Afterwards, if deemed resectable on CT
scan, we consider surgical removal. In these patients, we have >80%
of cats and dogs survive with a good quality of life for >1 year.
______________________________________________________________________
For further information on "Thymoma" or about any other cancer issue,
please call us (713-693-1166) or email Dr. Hahn at
drhahn@gulfcoastvetspec.com .
For more information on the web, use Medline at:
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Tumor Tidbits, April 2001. Volume 2, Number 5.