1) Canine cancer is a leading cause of death in dogs, with estimates of 100-275 cases per 100,000 dog-years. Preventive oncology aims to reduce certain cancer types through early intervention and identifying risk factors. 2) Mammary gland tumors are the most common tumor in female dogs, with risk greatly reduced through spaying before the first heat cycle. Hormonal exposure, age, breed, and weight can also impact risk. 3) For stray animals with advanced cancer that cannot be confined for prolonged treatment, euthanasia is supported to protect other dogs from potential transmission and avoid future suffering. Quality of life and animal welfare should be top priorities in veterinary decision making.

1. Canine Population Control:
Preventive Oncology and
Humane Care
Jessica Lawrence, DVM DACVIM (Oncology)
DACVR (Radiation Oncology) MRCVS
Head of Oncology
Royal (Dick) School of Veterinary Studies
University of Edinburgh

2. Canine Cancer
• Leading cause of death in dogs
• Estimates of incidence: 100-275 cases per
100,000 dog-years
• As in humans, cancer rate varies depending on
circumstances

3. Preventive Oncology
• Concept that aims to reduce the impact of
certain types of cancer on canine health
• Research that focuses on identifying risk
factors that can be used to improve early
intervention
– Continual application of new knowledge
• e.g. Routine Spay-Neuter programs

4. Cancer
• Accumulation of genetic abnormalities
(mutations) leading to uncontrolled cell
growth & proliferation
Criteria of from a variety of factors:
• Mutations can arise Malignancy
– Hormonal
• – Environmental
•–
Genetic
•
•
•

5. Mammary Gland Tumours
• Well established model of hormonal cause of
creating cancer
– “carcinogenesis”

6. Incidence & Signalment
• Most common tumor in female dog
– 0.2-0.3% incidence
– “Intact” registries, 50-70% of tumors
• Generally > 7 years old (median 10-11y)
• Any breed

7. Risk Factors
• Dependent on population
– Spay (OHE) status
– Age
• ↑ Risk with ↑ age
– Breed
• Genetics
– Body weight
• Fat may be source of estrogen

8. Risk Factors
• Hormonal exposure
– Early OHE significantly ↓ risk
• If OHE < 1st estrus, risk = 0.05%
• If OHE > 1st but < 2nd estrus, risk = 8%
• If OHE > 2nd but < 3rd estrus, risk = 26%

9. Hormonal Exposure
• Ovarian hormone exposure is
important in development of
mammary tumors
• Estrogens + progesterone
– Important for development of
mammary tissue
– Also increase growth factors +
mutations

10. Hormonal Exposure
• Greatest benefit on mammary tumour
prevention is if dog not allowed to go through
any heat cycle
– Pivotal and irreversible effect of ovarian
hormones early in life
• Exposure to exogenous hormones also ↑risk
– Differential role progestins vs. combination
estrogens/progestins

11. Biologic Behavior
• 50:50 “Rule”
– 50% benign, 50% malignant
– Of malignant tumours, 50% recur or spread to
other sites (“metastasis”)
• Larger = ↑ likelihood of malignancy

12. Biologic Behavior
• Metastasis
– Lymph node
– Lungs
– Liver/spleen
– Bone

13. Physical Exam
Benign Malignant
• Small • Ill defined
• Firm • Rapid growth
• Well circumscribed • Fixed
• Inflammation / edema
• Ulceration
• Pain

14. Physical Exam

15. Physical Exam

16. Physical Exam

17. Treatment of Choice
• Surgery
– Simplest surgery
• Lumpectomy, regional or chain mastectomy
• Lymph node assessment
• Dogs with malignant tumors at increased risk
of developing another malignant tumor

18. OHE at Surgery
• Controversial
– 2 recent studies suggested increased survival in
dogs undergoing concurrent OHE or OHE within 2
years of diagnosis of mammary tumour
– Decreases risk of ovarian tumors, uterine infections
– Perform OHE 1st
JAVMA 2005; 227;1625

19. Impact of Veterinary Intervention
• Given that most common tumour in the
female dog, OHE can make substantial impact
on population at risk
– Spay as early as possible for maximum benefit
– Theoretical benefit in older dogs
• Improves overall QOL in population at risk
– Limits influence of ovarian hormones

20. Cancer
• Accumulation of genetic abnormalities leading
to uncontrolled cell growth & proliferation
• Mutations can arise from a variety of factors:
Criteria of Malignancy
– Hormonal
– Environmental
•
– Genetic
•
•
•
•
•

21. Transmissible Venereal Tumour
(TVT)
• Transmissible sarcoma, Sticker’s
sarcoma, venereal granuloma
• Naturally occurring horizontally
transmitted infectious tumour
– Dogs but also other canids
– TVT and DFTD = only known transmissible
cancers that behave like infectious
parasitic neoplastic tissue graft

22. Incidence
• Widespread distribution
– Highest tropical + subtropical areas
– C. and S. America, India, SE Europe, China, Middle
East, Africa
– Environment where breeding is poorly controlled
• Areas with free-roaming sexually active dogs,
TVT is the most common tumour

23. Risk Factors
• Any age, breed, sex susceptible
– Endemic regions: usually dogs age 1-5 y at risk
– Very efficient transmission
– Licking, biting, sniffing, coitus
• Spontaneous regression possible in immune
competent & client owned dogs
– Usually starts within 3 mo
– Rarely occurs > 9 mo

24. Clinical Signs
• Primary lesions external genitalia
– Males: caudal penis >> prepuce
– Females: vestibule or posterior vagina
• Secondary lesions: head & face
– Severe and permanent damage
– Chronic discomfort
– Secondary bacterial infections

25. Treatment: Client Owned Pets
• TVT that does not spontaneously regress
responds to variety of treatments:
– Vincristine IV x 6 (most effective)
– Radiation therapy
– Surgery– 30-75% recurrence rate
– Analgesia should be part of thoughtful
therapeutic strategy

26. Impact of Veterinary Intervention
• Best strategy for population is prevention
– Stray dogs are a reservoir of “infection”
– Control of free roaming sexually intact dogs has
greatest potential impact on reducing TVT
• Minimizing impact of TVT improves QOL for
the population at risk and decreases overall
cost of veterinary services

27. Control
• Treatment: > 6-8 weeks to months
– Vital to keep animals sheltered and not roaming
– Incomplete treatment + release is not acceptable
– Neuter + release is not appropriate
• Euthanasia is valid and supported option for
stray animals that cannot be confined for
treatment:
– Protects wider population of dogs from TVT
– Avoids later suffering/ decreases existing pain

28. Veterinarian’s Oath

29. Veterinary Ethics
• (AVMA) Principles of Veterinary Medical Ethics:
– IIB: Veterinarians should first consider the needs of
the patient: to relieve disease, suffering, or
disability while minimizing pain or fear

30. Veterinary Oncology
• Principles:
– Primary Goal: Quality of life
– Secondary: Remission &
Survival
• Application:
– Financial commitment
– Requires adequate care
• How to apply to stray animals?

31. Quality of Life
• Lack of clinical work on QOL in dogs
– In humans: 20-50% at diagnosis; 70-90% with
advanced cancer
– ~ 30% of dogs at diagnosis experience pain? 80%
of dogs with end-stage experience pain?
• Euthanasia is rational and legitimate option
for animals in pain with advanced cancer
– Mammary tumours, TVT
– Any advanced cancer

32. Euthanasia
Every animal deserves respect, dignity and the
“5 freedoms”:
Freedom from hunger & thirst
Freedom from physical & thermal discomfort
Freedom from pain, injury and disease
Freedom to express normal behaviour
Freedom from fear & distress

33. Conclusions
• Simple steps such as routine spay/neuter
programs can have a massive impact on
population at risk & on lifetime cancer risk
• Animal welfare should always take centre-
stage when considering veterinary
interventions
– Quality of life measures
– Euthanasia is a sound and acceptable option if
benefit to population as a whole

34. Questions?
• Thank you!