강아지 중성화와 유선 종양 예방 증상과 원인, 진단·치료와 관리 포인트 총정리

Comprehensive Guide to Canine Mammary Tumors: Prevention via Spaying, Symptoms, Causes, Diagnosis, Treatment, and Management

Oncology/CancerDiseasesMeongsiljang Veterinary Advisory Board

The risk of mammary tumors in dogs varies significantly depending on whether they are spayed, making early spaying the key to prevention. This article provides a comprehensive guide to the causes, symptoms, diagnosis, and treatment options.

Canine Mammary Tumors Are Malignant Diseases That Can Be Prevented by Spaying

Early signs of mammary gland tumors in dogs

Canine mammary tumors develop from a combination of hormonal changes and genetic factors, with approximately half of cases in intact females being malignant. Exposure to hormones such as estrogen and progesterone, secreted by the ovaries, plays a significant role in tumor formation. In intact female dogs, the risk of developing mammary tumors increases with each recurring estrous cycle, leading to an incidence rate of about one in four. In contrast, performing spaying before the first heat cycle drastically reduces the risk of mammary tumors to nearly negligible levels. Early spaying is not just a routine surgery but a vital preventive strategy for saving lives. Therefore, it is important for pet owners to carefully consider the timing of spaying and consult with their veterinarian.

The Main Causes of Mammary Tumors Are Hormonal Imbalance and Genetic Predisposition

The primary cause of mammary tumors in dogs is prolonged exposure to hormones such as estrogen and progesterone, which are secreted by the ovaries. Repeated heat cycles and delayed spaying increase the risk of tumor development. Certain breeds, including Poodles, Spaniels, Dachshunds, German Shepherds, Terriers, and Setters, have a genetic predisposition and show higher incidence rates. Hormonal exposure can lead not only to simple physiological changes but also to malignant tumors, making early management essential. Additionally, obesity and excessive calorie intake can affect hormonal balance, with obesity in young dogs being particularly linked to an increased risk of mammary tumors. Therefore, lifestyle management and regular veterinary check-ups are key to prevention.

The impact of hormones on mammary glands

Check for the Main Symptoms and Signs of Mammary Tumors

Early signs of mammary tumors in dogs include small lumps and skin changes in the mammary area. Mammary glands should normally feel soft and pliable, so any firm lumps warrant attention. Early detection significantly improves treatment success rates.

Mammary Tumor Formation: Hard lumps may develop in one or multiple mammary glands, with posterior glands being more commonly affected.

Skin Changes: The skin over the tumor may become red, eroded, or ulcerate, particularly in malignant cases.

Size Increase: Lumps larger than 2 cm or growing rapidly are more likely to be malignant.

Pain Response: The dog may show discomfort or pain when the area is touched.

Weight Loss: As malignant tumors spread, overall vitality and condition may decline.

A dog suspected of having a mammary tumor

Symptoms Requiring Immediate Veterinary Visit

If the tumor grows rapidly, or if there is bleeding, discharge, or severe pain, consult your veterinarian immediately. Malignant tumors can spread quickly, so early diagnosis can save your pet’s life.

Mammary Tumors Are Accurately Diagnosed Through Ultrasound and Biopsy

Suspected mammary tumors are confirmed through fine-needle aspiration (FNA) cytology or tissue biopsy, in conjunction with a physical examination. Cytology and biopsy are essential for determining the tumor type, malignancy, and degree of differentiation, and are recommended prior to surgery. However, since cytology alone may not always allow for accurate grading, pathological examination of excised biopsy tissue is performed to assess malignancy and surgical margins. Ultrasound helps identify the lesion’s location and accurately guide sample collection. Additionally, chest X-rays or other imaging studies may be used to evaluate for lymph node or organ metastasis. Because an accurate diagnosis forms the foundation of the treatment plan, early screening is crucial.

The process of performing a biopsy on a mammary tumor

Treatment Methods Vary Depending on the Degree of Malignancy of the Tumor

For early-stage mammary tumors, surgical removal is the primary treatment. If there is no evidence of metastasis, the tumor and the affected mammary gland are surgically excised. Depending on the tumor’s size, location, and the extent of lymph node involvement, the surgeon may remove only the tumor, the entire mammary gland, or an entire row of mammary glands on one side. In cases of high-grade malignancy or metastasis, chemotherapy may be combined with surgery. For metastatic tumors, platinum-based chemotherapy has been reported to help extend survival. Radiation therapy may also be considered alongside other treatments for tumors that are difficult to resect or are extensive. The treatment plan is determined by the veterinarian based on a comprehensive assessment of the tumor’s characteristics and the dog’s overall health, and regular follow-up care after treatment is essential.

A puppy recovering after mammary tumor surgery

Home Care and Prevention: Timing of Spaying and Dietary Management Are Key

Spaying is the most effective way to prevent mammary tumors. When performed before a dog’s first heat cycle, it significantly reduces the risk to nearly negligible levels. The preventive benefit diminishes the longer you wait, so making an early decision is important. Additionally, excessive calorie intake can lead to obesity, and obesity during youth, combined with prolonged hormone exposure, is linked to an increased risk of tumors. A balanced diet and regular exercise help maintain a healthy weight and stabilize hormone levels. Regular checks of the skin and mammary glands are also important for detecting early changes. Since prevention is far more effective than treatment, proactive attention from pet owners is essential.

A balanced diet to help prevent mammary tumors in dogs

Timing of Spaying and Breed-Specific Precautions

Large breeds mature more slowly, so it’s best to delay neutering by one to two years. Some breeds have genetic predispositions that make regular check-ups essential. Always consult your veterinarian to create a personalized plan tailored to your pet’s needs.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Does not spaying guarantee that mammary tumors will definitely develop?

No. However, unspayed female dogs have a significantly higher risk, with about one in four developing mammary tumors. The risk increases with each heat cycle, so early spaying is recommended.

Can mammary tumors still develop after spaying?

Yes, it is possible. However, if neutering is performed during the young age, especially before the first heat cycle, the risk of occurrence can be reduced to almost negligible levels. Still, regular check-ups and early detection are important.

When is the best time to neuter a pet?

For the most effective prevention of mammary tumors, spaying before the first heat cycle is recommended. However, the ideal timing can vary depending on the breed and growth rate, so it’s best to consult with your veterinarian to determine the safest approach for your pet.

How long does recovery take after neutering surgery?

Most pets recover within 1 to 2 weeks. To support healing, keep an Elizabethan collar (e-collar) on to prevent licking at the surgical site and restrict excessive activity. Keep the incision area clean, and follow your veterinarian’s guidance for the specific recovery timeline.

What is the survival rate if the mammary tumor is malignant?

The prognosis varies significantly depending on the stage of the disease. If the tumor is small and there is no lymph node or distant metastasis, complete surgical removal in the early stages leads to a good prognosis. However, if the tumor exceeds 2 cm or has spread to the lymph nodes or other organs, the prognosis worsens. Therefore, early detection and regular check-ups are crucial.

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References

[1] The Dog Care Handbook, Things I Wish My Vet Had Told Me, 2024

[2] Handbook on Field Veterinary Surgery, Ch19: Ovariohysterectomy in Canines and Felines, 2023

[3] The Cat, Clinical Medicine and Management, 2nd Edition, 2022