Infection and Tumors of the Breasts in Cats
The cat normally has four pairs of mammary glands. The
upper two pairs have a common lymphatic channel and drain into the axillary
(armpit) lymph nodes. The lower pairs also have a common channel and drain into
the inguinal (groin) lymph nodes. Infections and tumors of the breasts may cause enlargement of the
corresponding lymph nodes.
This condition is most commonly seen in young cats. Unspayed female cats can
experience an enlargement of one or more breast glands that begins one to two
weeks after their first heat cycle. This condition, called mammary hyperplasia
or mammary hypertrophy, is caused by high levels of progesterone. Pregnant
queens also may experience mammary hypertrophy that begins during the first two
weeks of pregnancy. In a pregnant cat,
this needs to be distinguished from mastitis and mammary cancer. The condition has also
been reported in neutered females and males receiving progesterone therapy for
another condition, and will appear two to six weeks after the therapy.
The breast enlargement may or may not be painful. In severe cases,
characterized by rapid increase in breast size, there is reddish-blue
discoloration, warmth, pain, and ulceration of the skin overlying the swollen
breast. The hind legs may become swollen.
One very severe complication of mammary hyperplasia is clotting of the veins
in the breast. This occurs in a small number of cases. The clotting process
extends centrally. If the clots break free and are carried to the lungs, these
cats may die suddenly from pulmonary thromboembolism. Secondary
infections can lead to septic shock.
Treatment: The best treatment for mammary hyperplasia is spaying the
cat. When the condition is related to pregnancy or progesterone therapy,
consider either allowing the queen to deliver or discontinuing the
progesterone. The risks must be balanced against the benefits. Breast biopsy is
indicated only when breast swelling or enlargement occurs in a cat who is
neither pregnant nor experiencing her first estrous, or when the swelling does
not disappear after the source of the progesterone has been removed.
A new medication, aglepristone, is a progesterone blocker and removes the
hormonal stimulus for the problem. It has been used experimentally with good
success, but at this time it is not approved for use in the United States; it
may become available in the future.
Breast tumors occur frequently in unspayed cats. Eighty percent are
malignant (adenocarcinoma). The rest are benign adenomas. Breast cancer is the
third most common cancer in cats. Most affected cats are unspayed females over
6 years old. Siamese have an increased risk for mammary cancer, as do cats with
the calico pattern. Breast cancer is rare among spayed females, especially
those neutered before their first heat cycle. Early spaying reduces the risk