Breast cancer and mammary tumors are common in pets. Yes,
dogs, cats and small mammals may contract the dreaded disease as well as humans.
A non or late spayed female dog has twice to three times the chance (25%) of
getting breast cancer then a woman. Overall, 50% of tumors in female dogs are
Breast tumors can be malignant (cancer) or benign.
Malignant tumors spread all over the body and destroy vital tissues and organs
like lungs, liver, bones and more. Benign tumors, on the other hand, grow
locally and damage the adjacent tissues. Fifty-percent of breast tumors in dogs
and 85-90% in cats are malignant. Half of the malignant tumors and a large
portion of the benign tumors are stimulated by the female sex hormones and
therefore tend to be more aggressive on intact females. Dogs and cats usually
have eight to ten pairs of glands along the abdomen. Most tumors occur in middle
aged females and involve the rare two sets of glands. Mammary tumors in cats are
more common in old females and involve the front two pairs of glands.
Early detection is very important. Pet owners should always
be on the lookout for nodules, lumps or change in the consistency of the mammary
gland. Normal glands are soft and elastic. Any nodule or swelling should be
checked by the veterinarian as soon as possible. Chest x-rays and blood tests
are recommended preliminary procedures, as treatment might be pointless in case
of advanced tumor cells spreading and tissue damage. Once the preliminary tests
are negative, suspected tumors are removed or biopsied. The tissue sample is
sent to the laboratory for diagnosis. Life expectancy may increase if a
hysterectomy (spay) is done as well. Frequent follow-up exams and periodic chest
x-rays are needed to detect possible recurrences. Chemotherapy and radiation
treatment are of limited value.
Post-surgical survival time may range between several weeks
to several years, depending on the severity of the tumor. Large, fast-growing
ulcerated and deep tumors carry worse prognosis. Evidence of spreading to the
lungs (done by x-rays) or lymph nods (done by needle aspirate or a biopsy) also
indicates advanced stage of the malignancy.
Early spaying (before the first heat cycle) reduces the
risk of mammary tumors to 0.5%. If done after one period, the risk can be
reduced to 8% of that in intact female dogs. Spaying at maturity is much less
effective in preventing breast cancer.