Mammary tumors are observed as a solid mass or as multiple swellings underneath the belly. When tumors do arise in the mammary tissue, they are usually easy to detect by gently palpating the mammary glands. When tumors first appear, they may feel like small pieces of pea gravel just under the skin. They can grow rapidly in a short period of time and may double their size every month or so. The dog normally has five pairs of mammary glands. Although mammary cancer can occur in any of the glands, it is more common in the 4th and 5th glands (closest to the hind limbs). The only way to confirm if a tumor is malignant or benign is through diagnostics done by your veterinarian. The risk of malignant mammary tumors in dogs spayed prior to their first heat cycle is a miniscule 0.05%. The risk increases to 8% for dogs spayed after one heat cycle and jumps to 26% in dogs spayed after their second heat cycle.
It is very difficult to determine the type of tumor based on physical inspection. A biopsy or removal for histopathology is almost always needed to determine if the tumor is benign or malignant and to identify the type of tumor. Aggressive tumors may metastasize to the surrounding lymph nodes or to the lungs. A chest x-ray and physical inspection of the lymph nodes will help to determine if the tumor has already spread. Bloodwork and urinalysis as well as an abdominal ultrasound may also be recommended by your veterinarian.
Mammary tumors can be small, single nodules or large, aggressive, metastatic growths. With early detection and prompt treatment, many tumors can be successfully treated by your veterinarian. There are multiple types of mammary cancers in dogs. Approximately half of the mammary tumors in dogs are benign and the other half are malignant. The most common benign form of canine mammary tumors is actually a mixture of several different types of cells. This combination tumor in the dog is called a 'benign mixed mammary tumor' and contains glandular and connective tissue. Other benign tumors include complex adenomas, fibroadenomas, duct papillomas and simple adenomas.
Malignant mammary tumors include tubular adenocarcinomas, papillary adenocarcinomas, papillary cystic adenocarcinomas, solid carcinomas, anaplastic carcinomas, osteosarcomas, fibrosarcomas and malignant mixed tumors. Malignant mammary cancer can spread to the rest of the body through the release of individual cancer cells from the various tumors into the lymphatic system. The lymphatic system includes lymph vessels and lymph nodes. There are regional lymph nodes on both the right and left sides of the body under the front and rear legs. They are called the 'axillary' and 'inguinal' lymph nodes, respectively. New tumors may then form at these sites and then release more cells that go to other organs such as the lungs, liver or kidneys.
The cost of veterinary expenses varies widely for a variety of reasons, however, surgery to remove tumors may cost as much as $5000 or more depending on the size of the patient, health status and size of the tumor(s).
Mammary cancer is a very common cancer, especially in female dogs that were spayed at maturity, and can often be successfully treated, if caught early.
Follow-up exams may be necessary depending on the type of tumor and the type of surgery undertaken. Your veterinarian will likely prescribe a surgical cone and exercise restrictions while your dog recovers from surgery to reduce the risk of injury to the incision site.
Spaying female dogs before their second heat cycle greatly reduces their risk of developing mammary cancer. Regular physical exams may catch tumors while they are still very small.
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