Mammary tumors—my dog has breast cancer

Neoplasms of the mammary gland account for more than half of all cancers in female dogs. These benign or malignant tumors occur primarily in older, unspayed female dogs and initially appear as small, nodular changes along the entire mammary gland, which can later become very large. Different types of mammary tumors can occur.

INHALT
Anatomy, cause, and development Symptoms Diagnosis Treatment Forecast Prophylaxis
Anatomy, cause, and development

The mammary glands (= mammary glands) of dogs are arranged in two rows, the so-called mammary ridges, between the front and hind legs. Each mammary ridge consists of five (occasionally four or six) glandular complexes, each composed of a teat and the associated glandular tissue.

Although the exact causes of these tumors are unknown, several factors are suspected of influencing their development. For example, repeated use of sex hormones that suppress estrus increases the risk of benign tumors, whereas spaying the dog before her first or second heat has been shown to reduce the risk.

Since older female dogs are primarily affected, researchers assume that hormonal changes also play a role in the development of these tumors. Studies have also shown that small dog breeds are more commonly affected than large breeds, with poodles, cocker spaniels, dachshunds, and Yorkshire terriers being particularly at risk. A hereditary component cannot be ruled out either. Obesity can also promote tumor formation.

A tumor of the mammary gland causes degeneration and uncontrolled proliferation of glandular cells. More than half of all mammary tumors in female dogs are benign, with only 20 to 40% developing into malignant tumors. Like all malignant tumors, the latter spread very aggressively in the tissue and can metastasize (spread), in most cases via the lymphatic system to the regional lymph nodes and via the bloodstream to the lungs. However, mixed forms of mammary tumors also occur, in which benign and malignant cell areas can be found. This fact suggests that a benign tumor can also develop into a malignant tumor. Early detection and treatment of benign tumors is therefore essential to prevent metastasis.

Symptoms

The first lumpy changes in the dog's mammary glands are noticed when stroking the animal or during a routine veterinary examination, as the affected animals usually show no other signs of illness at the beginning. As the disease progresses, the growths become larger and can be felt and seen. Very large, aggressively growing tumors can severely impair the dog due to their location, so that lameness can occur, for example, if tumors are located close to the limbs. Large or very aggressively growing tumors can cause superficial skin or mammary gland inflammation. As the disease progresses, significant disturbances in general well-being such as fever, loss of appetite, or lethargy (= sleepiness) are also possible. If metastasis (= spread) to the lungs has already occurred, respiratory problems may also occur.

Diagnosis

As already mentioned, early diagnosis and treatment of mammary tumors are extremely important in terms of the chances of recovery. If you discover a lump in your dog's mammary gland, even if it is small and appears harmless, you should not wait too long but take your pet to a veterinarian as soon as possible. Based on your preliminary report and a clinical examination, the veterinarian will often be able to make a preliminary diagnosis.

However, a definitive diagnosis with classification of the tumor type can only be made after removal and examination of a tissue sample. With the help of fine needle aspiration, a method in which a special needle is inserted into the tumor tissue, small cell samples can be taken with a minimally invasive procedure. Furthermore, an X-ray examination can provide important information about any metastases (secondary tumors), especially in the lung tissue.

Treatment

For smaller tumors with a diameter of less than one centimeter, the veterinarian may initially recommend observation and close monitoring of growth. For larger and fast-growing tumors, surgical removal is the safest and most promising treatment. Depending on the type and extent of the tumor, different parts of the mammary gland are removed. Surgery that only removes the tumor tissue, known as nodulectomy (black circle), should be avoided as it often leads to delayed wound healing and recurrence. In a simple mastectomy, the tumor tissue is removed along with the affected mammary gland (red circle). In the case of particularly aggressive tumors, this operation can be extended to the adjacent mammary complex (regional mastectomy) and the local lymph nodes or even the entire mammary gland (radical mastectomy) (green and blue circle).

Schematic diagram of mammary tumors in dogs
1 Right milk line (blue circle) (the right and left milk lines represent the mammary glands) | 2 Local lymph node of the mammary glands | 3 Tumor of the mammary gland (black circle) | 4 Tumor and adjacent mammary complex of the tumor (red circle) | 5 Teat
Forecast

Benign tumors detected at an early stage have a favorable to cautious prognosis, depending on their extent. Tumors detected very late and growing aggressively, which have already metastasized, have a rather doubtful to unfavorable prognosis. In general, the earlier the tumor is detected and treated, the better the prognosis.

Prophylaxis

Since the causes of mammary tumors are not fully understood, their development cannot be completely prevented. However, it is known that early spaying of female dogs significantly reduces the risk of tumor development. Spaying before the first heat cycle reduces the risk almost completely, and spaying before the second heat cycle reduces it by a quarter. However, since early spaying is controversial for various reasons, you should always discuss such a decision with your veterinarian in detail beforehand.