Mammary tumors are frequently found in all mammalian species, but they are extremely common in dogs, affecting female dogs more often than the males. Among the domestic animals, dogs have the highest incidence of breast tumors. They are 3 times more common in dogs compared to women. Dogs are affected by many different types of tumors, but breast tumors account for half of them. Nearly 40% of the breast tumors in female dogs are cancerous.
The exact reason for the frequent occurrence of breast tumors in dogs is not known, even though it is found that their development is influenced by the female hormones. For example, they are found less frequently in male dogs than in females; and among females, those spayed before the onset of the estrous cycle are less likely to develop them. Their chance of getting these tumors is at par with that of the males too. Non-spayed dogs and those spayed later than their first heat have a significantly higher chance of developing tumors in one or more breasts.
A physical examination is sufficient to diagnose breast tumors, but a biopsy is usually done to confirm the diagnosis, as well as to determine the type of tumor. Mammary tumors may be treated in different ways depending on the type and the extent of their growth. Surgical removal of the affected breast, followed by radiation or chemotherapy, may be necessary if the tumor is cancerous. Benign tumors are usually cured by surgery alone.
Malignant mammary tumors may be fatal in most cases, with death occurring within a year of the appearance of the tumor. Spaying the female dogs before their first heat (estrus) significantly reduces the risk of mammary tumors. It should be considered for all female dogs that are not reared for breeding purposes.