How long do dogs live with mammary cancer? A Comprehensive Guide

To spay or not to spay

There is still the debate as to whether or not an OHE at the time of tumor removal in intact dogs improves survival time. Early studies did not support the recommendation of an OHE at the time of diagnosis. However, two recent studies were able to demonstrate a survival benefit for those dogs that were spayed at the time of diagnosis.1,4 It is logical to consider that an OHE would improve survival time since it removes the major source of estrogen and progesterone production. In a sense, it could be compared to using an anti-estrogenic drug such as tamoxifen. It would be expected that dogs that had estrogen or progesterone receptor positive tumors would benefit most from an OHE as this would eliminate a source of hormonal stimulation for any remaining tumor cells.

Prognostic factors

The prognosis for dogs with mammary cancer is not influenced either by tumor location or number of tumors. Other factors that are not prognostic are number of pregnancies, age at first pregnancy and occurrence of pseudopregnancies. The following are prognostic factors that have been shown in studies to predict survival or the disease-free interval.

Treatment of Mammary Gland Tumors in Dogs

Mammary gland tumors in dogs typically requires surgery. Chemotherapy and radiation can be used if the tumor is too large, has been incompletely removed through surgery, or has already metastasized, but surgical removal of the tumor is usually the treatment of choice.

Tumors that are not cancerous can most likely be left alone (unless cosmetically concerning or bother the dog) but should continue to be monitored for any changes in size or consistency.

There are five types of surgeries for mammary gland tumors in dogs:

  • Lumpectomy: removal of the mass
  • Simple mastectomy: removal of the mass and associated gland
  • Regional mastectomy: removal of the mass, the associated gland, and nearby glands and lymph nodes
  • Radical or unilateral mastectomy: removal of the entire mammary chain (radical or unilateral mastectomy)
  • Bilateral mastectomy: removal of both mammary chains (bilateral mastectomy)
  • Does My Dog Have Mammary Cancer? How Can I Tell? – Dog Health Vet Advice

    Mammary cancer and pyometra are important health hazards associated with ovary conservation in pet dogs. Early ovariohysterectomy may reduce the incidence of these two diseases, but an estimate of the extent to which the development of mammary cancer or pyometra adversely influences overall longevity is missing. As a first step toward addressing this knowledge gap, the results of a historical cohort study of Rottweilers that lived in North America are reported. Questionnaires completed by owners and veterinarians were used to obtain lifetime health and medical information on 242 female Rottweilers, including years of lifetime ovary exposure, age at death, and cause of death. To determine the extent to which longevity was shortened in females that developed these ovary-associated diseases, age-anchored life expectancy-defined as the median number of remaining years until death for females alive at specified ages during the life course-and years of life lost, a measure of premature mortality, were estimated. Mammary carcinoma was diagnosed in 19 (7.9%) females; median age at diagnosis was 8.5 years; case fatality was 37%. Pyometra was diagnosed in 16 (6.6%) females; median age at diagnosis was 5.4 years; case fatality was 7%. Median lifetime ovary exposure for the study population was 4.3 years. Although risk for developing both diseases increased with longer ovary exposure, longer ovary exposure (≥4.3 years) was also associated with an overall longevity advantage-a 33% decrease in mortality, living 17 months longer than females with shorter ovary exposure (P=0.002). Analysis of age-anchored life expectancy showed that at no time points during the life course was the current or future diagnosis of mammary carcinoma or pyometra associated with shortened survival compared to females who never developed these conditions. This lack of longevity disadvantage is an expected result for diseases with late-onset, moderate (<50%) case fatality (mammary carcinoma) or low (<10%) case fatality (pyometra). These findings fail to support the notion that a strategy, such as elective ovariohysterectomy, implemented to reduce the incidence of mammary carcinoma and pyometra will beneficially impact overall longevity. It follows that future efforts to find and implement effective longevity-promoting interventions should look beyond reducing the incidence of a particular disease to considering trade-offs.