Mammary tumors are very common in intact female dogs

50% are malignant and 50% are benign; of those that are malignant 50% have spread at the time of diagnosis

Surgery is the best treatment in most cases

Prognosis is dependent on the tumor type

What is it?

• Mammary tumors are the most commonly diagnosed tumor in intact female dogs that are older than 7 years of age
• Male dogs rarely develop mammary tumors
• Groups of tumors:
  • malignant cancer
  • benign cancer
  • unclassified tumors
  • hyperplasia/dysplasia
• 50% of mammary tumors are malignant and of these, 50% have spread at the time of diagnosis
• Inflammatory carcinoma is very malignant and comprises about 5% of all mammary tumors
• Benign tumors
  • are of great concern because they cannot be distinguished from malignant tumors
  • biopsy is the only test to help differentiate the type of tumor
  • keep in mind that dogs can have benign and malignant mammary tumors at the same time, therefore all masses should be evaluated by the pathologist
• Mammary gland hyperplasia
  • is a condition that causes lumps to form in the mammary glands during a dog's estrus cycle
  • as the hormone levels dissipate, the masses disappear
• Risk factors for mammary tumors
  • genetics have not been established as a risk factor, as is the case in humans
  • obesity
  • Spaying before the first heat results in less than 1% risk for developing these tumors
  • Spaying after the 3rd heat increases the risk to 25% for the developing these tumors
  • Spaying after the 4th heat has no sparing effect on mammary cancer, but reduces the risk of developing uterine tumors and a life-threatening infection of the uterus called pyometra

Signs

• Breeds prone to mammary cancer
  • Poodles
  • english Spaniels
  • English Setters
  • Terriers
• Signs a pet owner may notice
  • lump (mass) in the mammary glands
  • 4th and 5th mammary glands (closest o the groin) are commonly affected
  • color: norm, red or purple
  • consistency: soft or hard and sometime ulcerated
  • multiple masses
• Signs of an inflammatory carcinoma
  • very inflamed mammary chain (wide-spread)
  • severe swelling of the tissue
  • ulceration of the skin over the tumor in some cases
  • swelling of the hind or fore limbs
• Signs of spread of the tumor
  • lameness
  • breathing difficulty due to spread of tumor into the lungs
  • weight loss
  • poor appetite
  • malaise
  
  

Diagnosis

• Check the history of the dog's heat cycle - recent heat cycle could indicate a benign process
• General health check
  • Complete blood count
  • Chemistry profile
  • Urine testing
• Chest x-rays - to check for spread of cancer to the lungs
• Abdominal ultrasound - to check for spread of cancer to the internal abdominal organs
• Biopsy of mammary tumors and enlarged lymph nodes

Treatments

• Surgery
  • is an essential treatment for mammary tumors
  • one or more mammary glands are removed
  • if multiple mammary glands are involved, a radical mastectomy may be recommended
  • the tumor and a large zone (2 to 3 cm) of surrounding normal skin, fat and sometimes muscle are removed to reduce the risk of local tumor recurrence
  • tumors located is located in fourth and fifth mammary glands
    • skin flaps from the both flank folds may be needed to reconstruct the large wound following removal of the tumor
• Chemotherapy
  • may be recommended and is administered every three weeks via intravenous injection by our oncologist for a total of four to five treatments
  • treatments are typically done on an outpatient basis and may take a total of 90 minutes to complete each visit
  • unlike humans, most dogs do not lose their hair and usually have only mild side effects from the medication, such as transient loss of appetite and vomiting

Homecare

• Analgesics
• Limit exercise for 3 weeks
• Check the incision daily for signs of infection
• Recheck evaluation by the surgeon and oncologist 2 weeks after surgery
• Start chemotherapy 2 weeks after surgery if the incision has healed

Prognosis

• The biopsy report is the most important factor that will determine the prognosis
• Poor prognosis
  • invasion of tumor into adjacent normal tissue, blood vessels, lymph vessels and the lymph nodes
• Recurrence of tumors
  • grade 1 tumors is 24%
  • grade 2 tumors is 68%
  • grade 3 tumors is 90%
  • tumors larger than 3 cm have a 70% local recurrent rate versus 30% recurrence rate if the tumor is less than 3 cm
  • tumors that are less than 5 cm also yield a much better survival times (420 to 784 days versus 210 to 280 days)
• Ovariohysterectomy, at the time of mammary tumor removal, likely will not improve the survival of the patient

Complications

• Short-term complications are uncommon
  • temporary dehiscence (opening) of the incision
  • infection
  • tumor recurrence
  • spread of cancer

References

1. Alenza MDP, Tabanera E, Peňa.  Inflammatory mammary carcinoma in dogs: 33 cases (1995-1999).  JAVMA 219:1110-1114, 2001

2. Hahn KA, Richardson RC, Knapp DW.   Canine malignant mammary neoplasia: biological behavior, diagnosis and treatment alternatives.  J Am Anim Hosp Assoc 28:251-56, 1992

3. Misdorp W.  Tumors of the mammary gland.  IN: Tumors in Domestic Animals, ed. Meuten DJ, 4th ed. pp 575-606.  Iowa State Press, Ames, IA, 2002

4. Philibert JC, Snyder PW, Glickman N, Glickman LT, Knapp DW, Waters DJ:  Influence of host factors on survival in dogs with malignant mammary gland tumors.  J Vet Intern Med 17: 102-106, 2003

5. Rutteman GR, Withrow SJ, MacEwen EG.  Tumors of the mammary gland.  IN: Small Animal Clinical Oncology, eds. Withrow SJ, MacEwen EG, 3rd ed., pp 455-477.  WB Saunders, Philadelphia 2001

6. Waldron DR.  Diagnosis and surgical management of mammary neoplasia in dogs and cats.  Vet Med 96: 943-948, 2001