Cancer, it's not a diagnosis we want to either
give or hear, but all cancer is not created equal. Certainly
great strides have been made in the last decade in treating
canine cancer. However, before we have to deal with the
issue on an emotional level, I think it's helpful to step
back and look at the condition while our dogs are still
healthy, and consider what we'd do in any given set of
circumstances. For me the quality of an animal's life is far
more important than its quantity. Keeping an animal alive,
but in pain, seems selfish. They live in the here and now.
They remember the past. I don't think they would choose to
live in pain. Most veterinary oncologists realize this. For
this reason lower relative doses of chemotherapeutic drugs
are used on animals than on people, but they may still
experience severe gastrointestinal upset - diarrhea,
vomiting and anorexia - after each treatment. Most dogs do
not lose their hair as a result of chemotherapy. On the
other hand, removing an animal's limb is far less traumatic
to most dogs than it would be to us. I never cease to be
amazed at how well they bounce back even 24 hours after
surgery.
While veterinarians cannot predict the future,
the first question will be the benefit of various forms of
treatment. How long can the average dog with this kind of
cancer be expected to live, and what will be the effect of
treatment not only on life expectancy but on the dog's
quality of life? Like it or not, cost has to be considered
when considering treating cancer. The introduction of
generic chemotherapeutic agents has reduced this in some
instances, but it is still not going to be trivial.
In order to get a prognosis, tests have to be
done, and in general treatment should not be initiated until
a full work up has been completed. One of the first things
will be to look for evidence that the cancer has spread or
metastasized. The most likely location of secondary tumors
is the lungs, and so chest X-rays will be taken. If your
Beardie has a mast cell tumor, however, these rarely affect
the lungs, but frequently spread to the liver and spleen, so
X-rays or ultrasound of the abdomen would be in order. Lymph
nodes, particularly in the region of the tumor should be
evaluated. In order to identify the kind of tumor, and stage
it (see how it's progressing), it is necessary to perform a
biopsy. For many tumors, excision with clean margins will be
curative, but only with microscopic examination of the tumor
will it be possible to determine whether the whole thing has
gone. Unfortunately, this is rarely as simple as it sounds.
Clean margins means at least 3 cms. around the visible
tumor, even if the thing seems to shell out. Often the
visible tumor (especially a sarcoma) is surrounded by a
pseudocapsule of tumor cells, which may be left behind.
Incidentally, if radiation therapy is being considered in
addition to surgery, it is helpful if the surgeon places
surgical staples in the site when he operates, one of the
most frequent reasons radiation therapy fails is because it
is no longer possible to accurately locate the original
site. This is safe if megavoltage radiation is being planned
- which is more common - but can intensify the effects of
radiation with orthovoltage therapy, although it rarely
causes problems. Blood and urine should also be evaluated.
Bone marrow biopsy may also be helpful.
Multimodal therapy is frequently more effective
than relying on a single treatment method, and likewise drug
cocktails can be more effective, and reduce side-effects. As
well as surgery, radiation, chemotherapy, immunotherapy,
cryotherapy and hyperthermia may be recommended. Even if it
is not possible to remove the whole tumor, debulking it
makes it easier to attack with other therapies. However,
disrupting the blood supply of the remaining tumor may make
it less sensitive to other forms of treatment. Although it
delays surgery, preoperative radiation may shrink the tumor,
so that surgical excision will not need to be as extensive.
Lymphoma in dogs generally affects many if not
all the lymph nodes. However, more than 80% of cases go into
remission, with around a third of these living two or three
years on maintenance therapy. Spayed females live longer
than intact bitches. The choice of chemotherapeutic agents
is very important to the outcome for this disease. Treating
with corticosteroids (e.g., prednisone) prior to diagnosis
can destroy cancer cells, so that the extent of the disease
is not fully appreciated. More seriously, they can select
for resistant cells bearing the multiple drug resistance
gene which are immune to the effects of several chemically
unrelated cancer drugs - doxorubicin, vincristine,
actinomycin 1. All of these drugs can induce resistance, and
ultimately decrease overall survival time, although
improving the dog's condition in the meantime. Treating with
prednisone alone, the average prognosis is two months; with
COP (Cytoxan - cyclophosphamide*; Oncovin - vincristine and
prednisone) this increases to 4 to 6 months. The multidrug
protocol, using Adriamycin (doxorubicin) and/or L-asparagine
as well as COP increases the prognosis to 12 months with the
possibility of two year's remission. To maintain remission,
dogs may be given cyclophosphamide and Leukeran
(chlorambucil) possibly alternating with oral vincristine.
Routine lymph node inspections should be performed together
with blood counts to monitor bone marrow suppression. *
Cyclophosphamide can cause sterile hemorrhagic cystitis days
to weeks after administration. Pretreatment with mesna can
decrease the frequency and severity of the cystitis.
Sarcomas are tumors of muscle, bone and
connective tissue. Soft tissue sarcomas are common.
Typically they are locally invasive with potential
metastasis to both regional lymph nodes and distant sites.
They frequently recur after surgical excision, due to the
presence of neoplastic cells left in the pseudocapsule after
surgery. Microscopically the cancer extends along tissue
planes away from the original site. In dogs radiation
therapy after surgical excision results in local control
rates of 67 - 95% at one year. (In one study the four year
local control rate was 86% for a condition which has
historically been given a very poor prognosis.) Best success
is seen if radiation therapy is started two to three weeks
after surgery rather than waiting to see if the tumor
recurs. Some centers use intraoperative radiation therapy
with chemotherapy implant enhancement, using cisplatin or
carboplatin, to attack these tumors even more aggressively.
Postoperative radiation therapy may also be augmented with
chemotherapy using mitoxantrone, doxorubicin or carboplatin.
Osteosarcoma is diagnosed with X-rays of the leg.
It is best treated with limb amputation and postoperative
chemotherapy with carboplatin . (This is more expensive but
does not destroy the kidneys or produce as many
gastrointestinal side-effects as cisplatin which used to be
the drug of choice.) Average prognosis is 12 months. If the
lesion is small and towards the end of the leg local
excision (limb sparing surgery) may be attempted. However,
the prognosis is generally poor, with high infection and
recurrence rates.
Transitional cell carcinoma of the bladder may
spread to the urethra and prostate. Diagnosis is usually
delayed because the signs initially mimic cystitis, and by
the time it is diagnosed the cancer has usually spread over
such large areas surgery is not possible. Any case of blood
in the urine should be actively pursued. Chemotherapy with
mitoxantrone, Feldene (piroxicam) and Pepcid (famotidine)
produces a response in 50% of cases, reducing painful and
bloody urination for periods of 4 - 12 months.
Breast cancer is common in dogs. Provided it has
not spread to the lungs most veterinarians prefer to
conservatively remove the affected mammary gland. Some
however prefer to remove the whole chain either along one or
both sides. While there is evidence that this is necessary
in cats it has not been proven in dogs, although in many
instances the cancer will appear in other mammary glands it
usually does so randomly. Mitoxantrone is the preferred
chemotherapeutic agent for the treatment of mammary cancer.
Mast cells are connective tissue cells which
contain histamine and heparin (an anticoagulant) which are
important in the body's response to injury and infection.
Mast cell tumors are potentially vicious tumors no matter
what the grading particularly when located in mucous
membranes, groin, mammary tissue or urogenital region.
Tumors on the legs have a better prognosis than those on the
body. Wide deep surgical excision that does not perturb or
touch the tentacles of the tumor may be curative, but any
grade II or II tumor should also be treated with
postsurgical chemotherapy (prednisone and Vinblastine) and
or radiation therapy. If the tumor is staged local, well
differentiated and postoperative radiation therapy is also
given tumor free survival rates of two to five years of up
to 94% have been reported. For intermediate grade tumors the
figure drops to 50 to 75%. With surgery alone, recurrence
rates six months after surgery range from 25 to 76%
depending on the histological grade of the tumor. Radiation
therapy is useful for treating draining lymph nodes as well
as the tumor site, but if more extensive lymphatic
involvement has occurred chemotherapy is recommended. Poorly
differentiated tumors carry a very poor prognosis with a
high risk of recurrence. Radiation may be helpful to debulk
the tumor and make the patient more comfortable.
Many oral tumors may be treated by removal of all
or part of the upper or lower jaw followed by chemotherapy
with mitoxantrone or carboplatin. Median survival for dogs
after removal of the mandible (lower jaw) was 9 months for
malignant melanoma; 19 - 25 months for squamous cell
carcinoma; 10 - 12 months for fibrosarcoma; 5 -13 months for
osteosarcoma and a complete cure for epulides. Dogs with
squamous cell carcinoma of the tongue may survive for long
periods if the tip, up to one third of the length, is
removed. However, owners may have to hand feed some of these
animals depending upon the extent of the surgery. This is
often unpleasant for both owner and pet.
Nasal tumors result in high morbidity. Prognosis
is improved if they are discovered early and treated
aggressively with radiation therapy. Without treatment
average survival is 5 - 7 months. Even when treated less
than 50% survive for a year, and cataracts result from
treatment.
It is difficult to write about cancer because
treatments seem to change from day to day. It is not one
disease, and there are multiple causes, it should therefore
come as no surprise that different cancers carry different
prognoses. We are fortunate in New England to have available
the state-of-the-art radiation center at Tufts University
School of Veterinary Medicine. When we hear the word cancer
however, we run the risk of shutting down our minds and not
exploring the options available. Always ask about
alternatives, even if they aren't available at your
veterinarian's or in your area. If side-effects are
mentioned, ask about ways to avoid or at least minimize
them. Be sure to make thorough enquiries as to the prognosis
with all forms of treatment and the quality of life
associated with each. Prognosis can only be an average
though, some dogs will live longer and some shorter periods.
On the whole Beardies are stoic dogs. They will tolerate a
lot of pain we are probably unaware of. The best thing we
can do for our pets with cancer, or any other disease, is to
open ourselves to what they are telling us. If they aren't
having fun, and the prognosis is for more of the same or
worse, we have the ultimate gift of love which we can extend
to them. We can let them go, and take away their pain.