Last week I examined two patients for their one-year treatment anniversary. The first is a 16-year-old male neutered domestic short hair named Scooter, the other a 7-year-old female spayed Doberman named Emma. Both had been diagnosed with lymphoma.
Scooter presented originally with a two-month history of lethargy, intermittent anorexia, and progressive weight loss. He was FeLV/FIV and hyperthyroid negative. He had a palpable intestinal mass in the mid-abdomen.
Laboratory findings were nonspecific and included a nonregenerative anemia, moderate neutropenia and unremarkable serum chemistry. Abdominal ultrasonography confirmed a circumferential mass affecting the small intestine without nodal enlargement.
Cytological examination of cells obtained by ultrasonographic-guided needle biopsy of the intestinal mass showed numerous pleomorphic lymphocytes with occasional mitotic figures. Survey radiographs of the chest were normal.
He went to surgery that same day to have the segment of bowel removed. Biopsies were obtained from the liver, other areas of bowel and from two mesenteric nodes not previously observed on ultrasound. Later histopathology confirmed the lymphoma diagnosis with only intestinal involvement.
Emma presented originally with generalized enlargement of lymph nodes noted earlier that day by a groomer. Emma had no prior symptoms or problems.
Cytological examination of cells obtained by fine-needle aspiration biopsy of two lymph nodes showed a highly variable population of lymphocytes and a later core biopsy confirmed the diagnosis of lymphoma.
Clinical staging results from a complete blood count, serum chemistry profile, survey radiographs of the chest and abdomen were normal.
Lymphoma is one of the most common malignancies occurring in cats. Feline leukemia virus infection has been shown to be a significant cause of lymphoma in cats. As a retrovirus, FeLV can insert an oncogene into lymphocytes, resulting in uncontrolled growth of the cells (i.e. cancer). The disease may originate in any organ.
These tumors progress rapidly with widespread involvement eventually affecting all lymph nodes with significant lymphocytic infiltrates present in the liver, lung, kidney and bone marrow.
Because of the advanced stage at presentation (diffuse intestinal involvement, mesenteric lymph node enlargement, bone marrow involvement) and possible paraneoplastic syndromes (hypercalcemia, cancer cachexia), the lifespan of cats is short without treatment (30 to 60 days).
The cat with lymphoma can be successfully treated, but not cured, with chemotherapy. Many protocols exist that allow cats to enjoy a significant quality lifespan.
A positive test for FeLV indicates a poor prognosis. Because FeLV infects cells of the myeloid series, profound and sustained neutropenia can result following chemotherapy.
Like the cat, lymphoma is one of the more common forms of cancer affecting dogs of any breed or age.
The most-encountered anatomical form is generalized lymphadenomegaly without clinical symptoms (i.e., multicentric, Stage III). The onset is sudden and the prognosis poor (30 to 60 day survival) for most dogs.
Dogs in poor health (substage "b") have a poorer prognosis.
Chemotherapy is the mainstay for treating lymphoma in dogs and cats. I believe there are more protocols for lymphoma treatment than there are pets affected by lymphoma.
The selection of a protocol may depend on the clinical presentation, the medical status of the pet, or the economic budget of the pet owner.
Generally, the cyclophosphamide-vincristine-prednisone protocol is well tolerated, although side effects may occur and dosage or interval adjustments may be necessary.
Side effects of COP are infrequent but may include anorexia, vomiting and lethargy. It is a simple protocol, requiring regular treatment intervals of three to four weeks.
For dogs and cats I generally include asparaginase (Elspar) at every second or third vincristine visit and note a substantially longer remission, ranging from 12 to 18 months in most treated pets.
The most likely alternative to the COP protocol is the vincristine-cyclophosphamide-doxo-rubicin protocol. VCA is more dose-intense, treatments are weekly, and each drug is used five or six times during treatment resulting in greater risk of side effects and treatment delays.
However, once the 20-to 24-week protocol is completed, many pets enjoy another six to 12 months of drug-free remission. Including a protocol afterwards to maintain remission duration (e.g., asparaginase and cyclophosphamide) is controversial but many note longer responses.
Because Scooter presented at 16, had surgical removal of the intestinal mass, and had no other evident lymphoma, a four-week cycle COP protocol was used.
Every three months we reviewed chest and abdominal imaging, administered asparaginase, and at last week's one-year treatment anniversary we stopped further chemotherapy and celebrated his 17th birthday.
Because Emma was younger than Scooter and was in exceptional health, a VCA protocol was used. No problems occurred during the first two cycles and while there were no indications of heart disease or heart abnormalities, we replaced doxorubicin with mitoxantrone.
Mitoxantrone and doxorubicin have similar actions but the risk of drug-induced cardiomyopathy is substantially less. Emma finished the remaining four cycles without incident and returned every two months for physical examination.
The best protocol, in general, comes from assessing the physical and medical condition of the pet and attempting to eradicate as much cancer as possible without eradicating the pet's (or the pet owner's) quality of life.
Kevin A. Hahn, DVM, Ph.D., Dipl. ACVIM (Oncology), is director of Oncology Services at Gulf Coast Veterinary Specialists, Houston (www.gcvs.com/oncology), and is the oncology consultant for YourNetVet (www.yournetvet.com).