Solar-Induced Squamous Cell Carcinoma in Cats

Squamous cell carcinoma is a cancerous disease that most
commonly involves skin. Fair-skinned people tend to be
predisposed to this type of cancer after chronic, excessive
exposure to sunlight. Likewise, white or light-colored cats are
also susceptible to squamous cell carcinoma. Solar-induced
squamous cell carcinoma usually occurs in areas with little hair
coverage that are chronically exposed to sunlight. The most
common area affected in cats is the ear tip.

This disease occurs in older cats and may first become apparent
in summer, when sunlight exposure is greatest. The first symptom
of this disease that you will notice is reddening of the ear
tip. Other early signs of this disease include mild hair loss
and flaking of skin on the ear tip. Usually the first impression
is that your cat has psoriasis, in which the skin seems scaly
and inflamed. If caught early, these clinical signs may be
indicative of the precancerous form of the disease known as
actinic dermatitis.

A small skin biopsy is required to differentiate precancerous
actinic dermatitis from squamous cell carcinoma. It is best to
perform the biopsy procedure early because the clinical lesions
of squamous cell carcinoma are subtle and similar to this form
of dermatitis. One or both ears may be affected. If only one ear
is diseased, the other should be monitored closely because it
may also acquire the disease in the future.

Early, effective treatment of precancerous lesions may prevent
the onset of squamous cell carcinoma. Treatment for actinic
dermatitis includes sun restriction, especially during times of
peak solar intensity; water-resistant sunscreens with sun
protection factor (SPF) 15 or greater applied to the ear tips
twice daily; topical steroid application; and possibly oral
steroid or anti-inflammatory therapy.

The drug etretinate may also be used to alleviate symptoms. The
effect of etretinate is to decrease inflammation and skin
flaking while normalizing skin cell metabolism. Medical therapy
is not effective for lesions that advance to squamous cell
carcinoma, underlining the importance of early diagnosis for
suspicious lesions. Surgical removal of squamous cell carcinoma
of the ear tip (partial pinnectomy) is most effective when
performed as soon after diagnosis as possible. Early
intervention decreases the amount of the ear that must be
removed, because the lesion is smaller.

Early surgical removal also decreases the incidence of spread of
the cancer to the lymph nodes near the ear. There are different
surgical methods that are effective in removing the cancer. With
cryosurgery, like frostbite, the ear tip is frozen. The frozen
tissue dies and is removed. Although this method may be
effective, it is sometimes difficult to control the precise area
of tissue freezing. Freezing an inadequate area may lead to
recurrence of the cancer, and excessive freezing may result in
an unsightly appearance and be associated with excessive scar
and deformation of the remaining ear.

Laser surgery is available in veterinary medicine, but the
equipment is expensive and may be available only at special
referral facilities. Laser surgery provides precise removal of
the cancer with minimal, if any, side effects.

Finally, traditional surgical methods may be used to remove the
cancer. The procedure is similar to ear cropping in dogs, in
which part of the ear is removed with scissors and the skin
edges are sutured together. In cats with squamous cell carcinoma
of the ear tip, the veterinarian caring for the pet will remove
the cancerous ear tip and about one-quarter inch of
normal-appearing ear. A small amount of normal-appearing ear is
removed to ensure that the entire cancer has been removed.

You should insist that a pathologist evaluate the excised tissue
to make sure that the cancer has been completely removed. If the
biopsy shows that the cancer has not been completely removed,
further surgery should be performed. Incomplete removal of the
cancer at the initial surgery is not the fault of your
veterinarian. Microscopic evaluation of the tissue after special
processing is required to determine whether cancer cells are
present in the tissue. The naked eye is not able to make this
determination.

Cats tolerate the surgery well, and healing should progress
without complication. The healed surgery area will have more
hair than the ear tip, which will aid in preventing recurrence
of the cancer. Preventive care should be continued after
successful surgery.

In summary, prevention of precancerous actinic dermatitis is
recommended by limiting the outdoor activity of white or
light-colored cats to periods of nonpeak solar intensity.
Appropriate sunscreens should be applied to the ear of
pre-disposed cats who are outdoors during periods of peak solar
intensity. If your cat is diagnosed with actinic dermatitis, it
should be treated aggressively in the hope of preventing cancer.

Progression of actinic dermatitis to squamous cell carcinoma
requires surgery to remove the cancer. Because of availability
and financial considerations, most cats with this form of cancer
receive treatment consisting of traditional surgery. The
appearance of your cat’s ear after surgery will depend on the
extent of the disease. The ear may simply appear rounded at the
tip or require complete removal. If the entire ear is removed,
your cat will still be loved and cute with a striking
resemblance to “E.T.” of movie fame. Either result is far better
than uncontrolled spread of cancer to deeper tissues of the head.

The above is general veterinary information. Do not begin
any course of treatment without consulting your regular
veterinarian. All animals should be examined at least once every
12 months.