Decision Making in Feline Cancer Patients
David J. Argyle, BVMS, PhD, DECVIM-CA (Oncology), MRCVS
Royal (Dick) School of Veterinary Studies Hospital for Small Animals
Easter Bush, Midlothian, UK Introduction
This short presentation will describe approaches to these diseases,
standard treatment protocols and advances in radiation and chemotherapy-based treatments. Particular emphasis will be placed
upon the
special considerations in cats with regards drug metabolism, nutritional support during therapy and prognosis of individual diseases.
Feline Lymphoma
Diagnosis and Staging
The various anatomical forms of feline lymphoma (mediastinal, alimentary, renal, multicentric
and extranodal) have been well described.
Alimentary--characterised by gastric, intestinal, or mesenteric lymph
node
involvement, this is one of the
more
common forms of feline lymphoma.
Gastrointestinal lymphoma
may present as a solitary mass lesion or as a diffuse
infiltration of extensive
areas of bowel. Clinical signs are non-specific, including anorexia,
vomiting, and diarrhoea. Animals previously diagnosed with lymphoplasmacytic
gastroenteritis have been reported subsequently to develop gastrointestinal lymphoma. Most
cats with
alimentary lymphoma are FeLV ELISA negative.
Mediastinal--most cats with mediastinal lymphoma are relatively
young and FeLV ELISA positive.
Typical clinical signs include dyspnoea and exercise intolerance due to the presence of the
space-occupying lesion and pleural effusion.
Coughing may occur secondary to compression of the
trachea by the
large mediastinal mass.
The
heart sounds may
be muffled
and caudally displaced.
It is often abnormally difficult to 'spring the ribs' of the cranial
thorax of affected young cats.
Multicentric--unlike the situation in dogs, this is
a relatively
uncommon form of feline lymphoma.
It must be distinguished from various forms of generalised reactive lymphadenopathy, including some forms that
occur in retrovirally-infected cats. Fine needle aspiration
can sometimes provide a definitive diagnosis, but cutting needle biopsy or excisional
biopsy may be necessary.
Extranodal--the extranodal form includes all lymphomas
that do not fall
into any of the preceding
categories and accounts for
approximately 5% of lymphoma in
cats. Ocular, neural, renal, and cardiac forms are the most
common sites of involvement.
Treatment and Prognosis
In most parts of the
world, lymphoma is by
far the most common feline malignancy
and there have been numerous reports on treatment and prognostic factors. Lymphoma should
be regarded as a systemic disease, and in
almost all forms of the disease
chemotherapy is appropriate; either alone or as an adjunct to surgery and/or radiotherapy. Numerous treatment protocols have
been
described for
feline lymphoma. Most use vincristine, cyclophosphamide and prednisolone as the core drugs. Doxorubicin is also an important,
effective drug.
The prognosis for cats with lymphoma
is reported to vary according to anatomical form of disease, FeLV status, presence or absence of azotaemia, presence of peripheral
blood cytopenias, and chemotherapeutic
protocol used. FeLV negative
cats that achieve a complete remission following
induction therapy are likely to
have durable (i.e., > 6 month) responses, particularly when doxorubicin was included in the
chemotherapy protocol. However, FeLV positive
cats have significantly shorter
remissions and survival
times when treated with available
chemotherapeutic protocols.
The overall
response rate in cats is somewhat poorer
than
in dogs. Intriguingly, prognosis may
also be
changing over time.
The
protocol to which most others have
been
compared is COP. Currently, for most feline lymphoma cases the
25 week Madison-Wisconsin protocol appears to give the longest
duration of remission.
This is a finite protocol that does
not include maintenance therapy. The exception is
small cell lymphoma of the GI tract. This is treated continuously with a protocol including every other day prednisone, and chlorambucil given at 20 mg/m2 every two weeks.
Feline Squamous Cell Carcinoma
This is a common skin tumour that
accounts for approximately 15% of cutaneous
tumours in the cat.
They are usually located on non-pigmented skin and in areas
that are not
covered with hair. In many instances there is a recognized
solar exposure relationship and these tumours are often referred to as
'actinic' SCC.
Presentation
In the
cat,
lesions occur most
commonly on the
head
including the nasal planum, eyelids, temporal
region, and pinnae. Multiple
lesions are present in 30% of cats. There is typically a progression of lesions from actinic keratosis
to squamous cell carcinoma in situ to squamous
cell carcinoma.
Squamous cell carcinoma
can present as a proliferative or ulcerative/erosive lesion. The proliferative
lesions vary in their appearance
with some forming red firm plaques or cauliflower appearance that may ulcerate. The erosive lesion most
commonly seen in the
cat initially starts as a shallow crust
that may
develop into a deep
ulcer.
Early lesions most
notably in cats appear to be small pinpoint scabs that may
even heal then recur. Tumours can be locally invasive but
are
late to metastasize. The degree of invasion can be quite
severe and response
to therapy is usually better with early lesions (Tis
to T1).
Surgery and Cryosurgery
Remains the
treatment of choice although there are numerous reports using other modalities. In the cat, lesions of the pinnae are more manageable than the nasal planum due to location (i.e., more aggressive
surgery can be performed).
Wide
surgical excision
of other sites is also recommended
but again, prognosis and the
chance of recurrence
are dependent on the tumour stage.
Chemotherapy
Chemotherapy has shown little consistent
efficacy in the veterinary literature. Agents that
have been
used include mitoxantrone, actinomycin D.
Radiation
Cats with actinic keratosis,
carcinoma in situ and early SCC lesions less than 2 mm in depth respond well to plesiotherapy (form of superficial radiotherapy). In a group of 25 cats treated with a single, high dose utilizing strontium-90, 90% were free of tumour 1 year following
therapy. The mean disease-free
interval was 34 months. For cats with more advanced lesions, external beam radiation is recommended.
Photodynamic Therapy
If applied to early
lesions, results are generally positive.
Feline Mast Cell Disease
Splenic Mast Cell Tumours
MCT primary to the spleen
in cats is most common in older non purebred cats. Signs include nonspecific illness
or chronic vomiting due to histamine
release causing gastroduodenal ulceration. Liver, lymph
nodes and bone marrow are also commonly affected. Staging includes a CBC, biochemical profile, urinalysis,
FeLV,
FIV, thoracic radiographs, abdominal ultrasonography and bone marrow aspirate. Fine needle aspiration
cytology or biopsy of spleen is indicated. The diagnosis is sometimes made from ascitic
fluid or blood smear.
As initial
treatment, splenectomy normalizes other disease
within 5 weeks. The median survival is 12 months. As adjunctive
therapy, the use of corticosteroids
is controversial. Chemotherapy (CCNU, vinblastine) has not
been
reported. Supportive
therapy consists of preoperative H1 and H2 antihistamines to reduce risk of gastrointestinal damage and shock especially during surgery. The same drugs may be palliative for clinical signs but
results are variable.
Intestinal Mast Cell Tumours
Intestinal MCT are most
common in small intestine, causing
vomiting, inappetence and weight
loss. Staging is the same as splenic MCTs. Metastasis is very common. Prognosis is poor. Initial treatment consists of wide surgical excision including
5-10
cm of normal bowel.
Adjunctive therapy has not
been described, but
consider chemotherapy with prednisone or CCNU.
Cutaneous Mast Cell Tumours
Cutaneous MCTs are common in all age cats; and Siamese are
predisposed. Tumours are usually solitary but can be multiple and may
often be hairless
and
firm. Tumours occur most
commonly on the head and neck. Cutaneous
MCTs in cats need to be differentiated from eosinophilic granuloma.
Systemic involvement is rare. Staging includes a CBC, biochemical profile, urinalysis,
FeLV,
FIV and excisional
biopsy for solitary
lesions. Histologic grading does
not predict clinical behavior.
If multiple lesions are present,
thoracic radiographs, abdominal
ultrasonography, buffy coat smear and bone marrow aspirate are necessary to rule out
systemic disease.
Surgical excision is usually curative but
new
lesions may arise. Spontaneous
regression has been
reported in Siamese cats with histiocytic MCTs. Adjunctive
therapy for incompletely excised tumours
consists of radiation therapy.
Corticosteroids are probably not
effective. Other chemotherapy has not been reported but vinblastine or CCNU could potentially be useful.
Vaccine-Associated Sarcoma
Vaccine-associated sarcoma in cats is a complex
disease with a poorly understood
pathogenesis.
Decision Making: Vaccination
The epidemiological evidence puts vaccination as an inciting
cause for this disease. Consequently, recommendations are now in place to promote prevention
of the disease, or at least early detection.
These include:
Avoiding the
interscapular space
Subcutaneous rather than intramuscular vaccination (early detection) Rabies/FeLV vaccine on the distal
limb
Other vaccines on the
distal shoulder
Decision Making: Post Vaccination Lumps
Some Rabies and FeLV vaccinations will produce post-vaccination lumps
in nearly 100% of cats
vaccinated. Most of these will resolve over a 2-3 month period, and most vaccine-associated sarcomas
will not occur prior to 3 months following
vaccination. Consequently it is
recommended that all
post-vaccination lumps
be removed if still present at 3 months (or if they grow beyond 2 cm, before 3 months). Surgical biopsy is recommended prior to definitive removal.
Decision Making: Vaccine-Associated Sarcoma
Once a vaccine-associated tumour develops, management and control can be difficult. Below is a summary of appropriate steps:
Pre-surgical biopsy is highly recommended
Complete staging:
Blood count and chemistry
Urinalysis
Thoracic radiography
MRI or contrast
CT is highly recommended for accurate surgical assessment of the extent of disease
Single surgical
excision, even with wide margins, is
rarely curative for vaccine-associated sarcoma. Local recurrence
is common and a second
surgery is always difficult.
However, for lesions on limbs,
amputation would appear to have
a higher success rate that single surgeries for VAS in
alternative sites. Radiotherapy has been shown to improve on surgery alone. Two options are available:
1. Pre-operative radiotherapy: (has been shown to give local control to 23 months)
2. Post-operative radiotherapy (control to 12 months in 1 study)
The author's
standard protocol is to pre-operatively treat cats to 48 Gy using cobalt 60.
For
cats with tumours that overlie
vital organs such as kidney, we recommend
treatment with electrons using a linear accelerator. The advantage of pre-surgical radiation is that the
radiation field is much
smaller and easier managed. Following radiation surgical
excision is performed and margins examined for completeness of resection.
At surgical excision margins are tagged and/ or dyed with Indian ink.
The Role of Chemotherapy
For animals
who
do not undergo radiation, or whose margins are in doubt after radical
surgery, or who have metastatic disease, chemotherapy may
be offered as an adjunct. For patients that
have had wide surgical excision following radiation, the
addition of chemotherapy would appear to have little
benefit. For cats that
do not have
radiation but have surgery alone (with curative intent), the
addition of chemotherapy would appear to improve the time taken for recurrence. Drugs that have been used include Adriamycin (doxorubicin), carboplatin, Doxil (liposome encapsulated doxorubicin). There is no benefit of Doxil over doxorubicin.
No comments:
Post a Comment