Cancer is the biggest geriatric disease we face. In fact, half of our patients more than 10 years old will die from it. Surveys show that pet owners regard cancer as their greatest fear. Some will prepare for it while others don't think about it or reject treatment as an option, preferring to let "nature take its course."

The fate of older pets with cancer is determined by the very first choices made by the caregivers and veterinarian who first suspects that pet has cancer. Therefore, it is important that practitioners know about oncology recognize and treat it properly in its early stages.

The most common tumors in senior dogs and cats are reviewed here. They are cutaneous, mast cell and lymphatic tumors. Mammary, skeletal, oral and visceral tumors will be addressed in the coming months. Every pet on chemotherapy gets CBCs and platelet counts to monitor for myelosupression.

Cutaneous Tumors and FNA
Skin tumors are obvious to clients, who often bring in their pet solely for the doctor to examine the lump. Skin tumors always require professional inquisitiveness with fine needle aspiration (FNA) cytology to answer the questions that clients ask: "Is this lump a problem for my dog? What is this lump? Should it be removed?"

FNA answers these questions scientifically. We owe it to the client to answer if this lump is a mast cell tumor or not. It's puzzling why one would pass up the opportunity to run a FNA on almost every lump seen in practice. Lipomas are easy to confirm via the FNA yield of clear grease on the slide, without microscopic exam.

For lipomas, we can assure clients that surgery is not needed unless the size of the mass interrupts locomotion. If blood is aspirated from a mass, without history of trauma, it should be removed for biopsy. If the skin mass is firm or fixed and cells won't exfoliate, further steps to harvest cells are required. I like to use an 18-gauge needle and run it in and out on the same track and then angle it to "chop" a tube or core of cells that can then be aspirated from the mass for cytology.

Most sarcomas will yield cells for study with this technique. If no cells are harvested with the 18-gauge chop technique, then a punch or true cut biopsy is the next step. The patient should not leave this first office call without FNA diagnosis or recommendation for a biopsy.

Mast Cell Tumors
Mast cell tumor (MCT) is the most common malignancy in dog skin. It is poorly understood because despite attempts to grade the individual tumors, they don't behave predictably. I call mast cell cancer the "trickster."

The Veterinary Cancer Society (VCS) held its first mid-year focus meeting on mast cell cancer in 2000. It was concluded that MCT may be dormant for years. MCT may mimic lipomas or any other lump, therefore FNA should precede surgery.

The surgery should be planned with wide, 3 cm surgical margins whenever possible or at least with margins as large as the tumor itself on all planes. If the draining lymph node and margins are clean with adequate borders and it is Grade I, 50 percent are cured with surgery. Anything other than this needs more attention.

Clients need to be fully informed about MCT and the potential of recurrence in the future. As practitioners, we owe the client a full understanding of what the histopathology report contains. If narrow or dirty margins are evident on the report, advise clients that a second surgery to "clean" the tumor bed of tumor "tentacles" is needed or that radiation therapy or a combination of both is indicated.

If the tumor appears in the axilla, mammary tissue, groin, perineum, genitalia or in any of the mucocutaneous tissues, it behaves biologically as a Grade III with a high rate of recurrence, metastases and fatality (even if the report fails to comment on this behavior).

It is important to present an accurate consultation at the start. Proper advice gives clients a chance to declare war on cancer before an insidious recurrence wins the battle. Clients do not appreciate their pet's biopsy report being filed away without their full awareness of its information regarding margin determination or recurrence.

Intraoperative radiation therapy and intralesional depomedrol or triamcinolone are adjunctive therapies that enhance the reach of surgery. VCS members were divided as to the importance of bone marrow, splenic and hepatic aspirates in early case workup and agreed that buffy coat smears were worthless. There was agreement that if radiation therapy was elected, a work-up was needed.

Chemotherapy protocols for mast cell cancer range with stage and grade of disease. We use Prednisone at 40 mg /M2 PO q 48 hours for 10 to 14 days then 20 mg/M2 q 48 hours along with chlorambucil at 4 to 6 mg/M2 q 48 hours for maintenance of dogs with mild clinical disease.

Vinblastine at 2 mg/M2 or vincristine at 0.7 mg/M2 I.V. weekly for six weeks then every other week and every three weeks as maintenance may be added to the above protocol for high-grade or metastatic disease. If chlorambucil is not effective, Cytoxan at 200 to 300 mg/M2 given PO over a four-day period may be used on the alternate weeks when not using the I.V. vinca alkaloids.

Lomustine at 50-85 mg/M2 divided into 2-3 doses given orally over a four day period and repeated every 21 days is my first choice for advanced disease. It causes significant myelosupression after three to four cycles, so I increase the interval between treatments to five to eight weeks apart. Lomustine is one of the few drugs that has proven efficacy against mast cell cancer.

Cats seldom get MCT. When they do, it appears facially. It is more common in Siamese. Lumps (other than warts) on senior boxers, Boston terriers, Shar Peis, bull mastiffs and golden retrievers always need FNAs and anticipatory case management.

Lymphoma
Canine and feline lymphoma is one of the most frequently seen and dramatic malignancies in everyday practice. Ten years ago, the National Cancer Institute (NCI) reported that exposure to 2-4 d (a common weed killer) caused lymphoma in dogs. FeLV and FIV puts cats at risk for lymphoma. There may be other factors that induce the mutations seen in canine lymphoma, however no viral isolates similar to HIV, FeLV or FIV have been confirmed as the causative agent in dogs.

Generalized or localized lymphadenopathy commonly indicates canine lymphoma.

Older cats often test negative for FeLV. They present with abdominal masses, enlarged mesenteric lymph nodes or infiltrated or obstructed intestines often following inflammatory bowel disease (IBD). FNA must become an automatic reaction when enlarged lymph nodes are discovered.

I prefer the new methylene blue stain to look at FNA smears for cytology because it is quick. Clients receive a tentative diagnosis immediately while waiting for the panel, urine analysis and confirmation of the cytology. Regarding options for chemotherapy protocols, it may be best to refer the case to an oncologist for a consultation.

I tell clients that lymphoma is my favorite disease to treat. We see 85 percent complete remissions and a nice quality of life for typically one year. Cats with lymphoma also do well on the chemotherapy protocols if they are not too debilitated at presentation.

In my practice, one third of those pets that remain in remission at one year may go on to live several years or live out a natural life span. Protocols do vary with the clinician.

I often tailor a modified basic Wisconsin protocol to suit my client's travel and finances. Prednisone is decreased over three weeks and only on cytoxan days to promote fluid intake. We give L-asparaginase on the first day and administer vincristine at 0.7mg/M2 I.V. on week number one, number four and monthly as maintenance until 18 months. Cytoxan is given PO at 200 mg/M2 divided over two days on week number two and number five. Adriamycin is given I.V. at 30 mg/M2 in medium to large dogs and at 1 mg/kg in small dogs less than 20 pounds on week number two and number six.

I don't often use methotrexate. I prefer PO cytoxan to rotate with chlorambucil at 1.4 mg/kg divided over 24 hours 14 days after the monthly vincristine maintenance.

Doses must be modified to the approximate lean weight in fat pets. If the patient has a high tumor burden, fever, weight loss, anorexia, hypercalcemia, renal or hepatic dysfunction, the induction should be given over several days during hospitalization with intense supportive care consisting of 24-hour I.V. fluid therapy, vitamins, hand feeding and antibiotics.

Dr. Villalobos, the Leo Bustad Companion Animal Veterinarian of 1999, is the editor-in-chief of the American Association of Human Animal Bond Veterinarians Newsletter. She owns Animal Oncology Consultation Service in Woodland Hills and a partnership with VCA Coast Animal Hospital and Cancer Center in Hermosa Beach, Calif. Her e-mail is dralicev@aol.com.