WEB Vetnews May 2015

Mei/May 2015

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Squamous cell carcinomas

(SCC) in dogs and cats

This cancer is caused by high levels

of exposure to the B-fraction of ultra-

violet radiation (UVB), on susceptible

non-pigmented animal skin. South

Africa has one the highest UV levels

recorded in the world. Factors that

influence UVR levels across the globe

include altitude, intensity and duration

of sunlight, and the thickness of the

ozone layer. The UVB energy enters

the basal cell of the epidermis and

mutates the DNA, which results in

the uncontrolled proliferation of the

squamous cells. The normal histology

of the well-ordered squamous cell

tissue changes from its regular pattern

to one of disintegration, ultimately

leading to the development of a SCC.

Typically the clinical lesions are

treated with linear accelerator electron

radiation therapy with/without surgery.

The earlier this condition is recognised

and treated the better the prognosis.

To prevent the solar exposure in dogs,

ultra violet Lycra body suits are worn

(9 different

sizes and

male/female

are available)

together

with a long

acting 8 hour

sunscreen.

Cats are

naturally

nocturnal

animals, so the

cats that are at

risk should be

confined to the

sunniest room

in the house, with a special plastic

film that blocks the UV, but allows the

visible light and infrared energy to

pass through. The cats are fed in this

room at 08:00 and released at 17:00.

Cutaneous Mast Cell Tumours

(MCT)

MCT are visibly the most difficult

tumours to judge and a fine needle

aspirate of any suspicious “lump”

should be examined; confirmation

using a biopsy may be needed .

The pathology report is useful for

understanding how aggressive the

tumour is, by its mitotic index and

the description of the cells. Often the

pathologists do not grade the tumour,

as the prognosis and the eventual

outcome are vastly different. Radiation

for the primary cutaneous tumour is a

most effective way to consolidate the

tumour before surgery. If the tumour

has metastasized (detected by use of

ultrasound examination) both radiation

for the primary and chemotherapy for

the secondary tumours is necessary.

The MCT

patient

shown in

the photo

graphs was

graded as

Grade 3 and

yet did not

metastasise;

some of the

Grade 2 MCT

did meta

stasise.

Soft tissue sarcomas

are derived from the

mesenchymal cells

There are many tumours in

this category, e.g. liposarcoma,

chondrosarcoma, fibrosarcoma ,

peripheral nerve sheath tumours

and more. Biologically they generally

behave in a similar way; usually

they are found in the subcutaneous

tissue, they grow slowly, usually

do not metastasise, but often

recur after surgical excision. These

tumours require very wide surgical

margins as they are surrounded by a

pseudocapsule that allows the cancer

cells to escape. If they are radiated

pre-operation (consolidation), they

are easier to remove in their entirety.

It is easy to make the radiation field

very much larger than the surgical

field and if the area is also radiated

post-surgery, the success of the

treatment is greatly enhanced.

Because these tumours grow more

slowly than carcinomas, they require

a higher total dose of radiation.

Although in humans the radiation

doses have different limits for the

different types of tissue, this has not

yet been described in the dog and

cat.

For successful treatment of cancer

in dogs and cats remember the

following:

• Early diagnosis is essential

• Educate pet owners to recognise

the following

- small non-healing skin lesions

specially in non-pigmented skin

- lumps in abnormal locations

The most gratifying effect of radiation

for the animal and their owner is that

of the palliation of pain. The previously

depressed animals start eating, playing

and grooming again.

Acknowledgements

• Colleagues for your referals and the

care of your patients.

• Liesl du Raan (radiation therapist)

for expertise, interest and unfailing

care for each patient.

• Scientists whose work I have read.

• You, the reader for your interest.

Mast Cell Tumour, Grade 3

The first photograph shows the MCT at presentation; the second

photograph was taken three years later, after radiation, surgery and post-

surgery radiation (total radiation 10 x 3 = 30 Gys)

Histiocytoma

The first photograph shows the tumour at presentation, patient not

eating. Treated with radiation therapy (12 x 2 Gys). Second photograph

taken 80 months later, no recurrence.

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