NDWC Chennai 2013 - Canine Polulation Control Preventive Oncology & Human Care - Jessica Lawrence


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  • Worldwide Incidence = 2-3 tumors detected per 1000 dogs at risk, usually intact female dogs Incidence in the US is lower than in many other countries due to the common practice of OHE at a young age Ultimately most studies especially those that are insurance based may underestimate the true incidence of disease especially if the diagnosis and registration required surgical biopsy Some dogs at risk: spaniels, English setters, pointers, fox terriers, bostons over-represented in the literature
  • Dogs spayed < 1 st estrus have risk of 0.05% Dogs spayed > 1 st estrus before 2 nd have risk of 8% Dogs spayed > 2 nd estrus risk increases to 26%
  • Both estrogens and progesterone are important for normal mammary gland development and maturation. Mammary glands undergo distinct clinical and histopathologic changes as hormone levels fluctuate according to the phases of the estrus cycle Estrogens and progesterone are mitogens of mammary epithelium and induce proliferation of intralobular ductal epithelium and development of ducts and lobules, thereby causing expansion of the mammary glands. Research in humans has suggested that estrogen and its metabolites lead to enhanced production of growth factors through receptor binding but also have direct genotoxic effects by increasing mutations and inducing aneuploidy independent of estrogen receptor status.
  • Dogs treated with progestins to prevent estrus have a higher risk of developing mammary tumors compared to dogs not receiving treatment Most studies suggest that low dose progestins increase risk for benign tumors whereas combination of estrogens and progestins increases malignant tumors
  • Note: not all malignant tumors will have these features
  • In theory, OHE may be of assistance if hormone-dependency is an unrealized factor as it removes the influence of progesterone and estrogen
  • One study out of China in 2005 that demonstrated a statistical benefit in spayed dogs at 2 years after diagnosis of mammary tumor however other studies have not supported this. While there is no clear benefit to spaying the dog, there is theoretical benefit from removing the influence of progesterone and estrogen.
  • Extragenital lesions can lead to a variety of signs including sneezing, epistaxis, epiphora, halitosis, tooth loss, exophthalmus, skin masses, facial deformation and regional LN enlargement Lesions vary in size (2-3 mm - 15 cm) Firm, friable, inflammatory, hemorrhagic Secondary bacterial infections Chronic discomfort
  • NDWC Chennai 2013 - Canine Polulation Control Preventive Oncology & Human Care - Jessica Lawrence

    1. 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. 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. 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. 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. 5. Mammary Gland Tumours• Well established model of hormonal cause of creating cancer – “carcinogenesis”
    6. 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. 7. Risk Factors• Dependent on population – Spay (OHE) status – Age • ↑ Risk with ↑ age – Breed • Genetics – Body weight • Fat may be source of estrogen
    8. 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. 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. 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. 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. 12. Biologic Behavior• Metastasis – Lymph node – Lungs – Liver/spleen – Bone
    13. 13. Physical Exam Benign Malignant• Small • Ill defined• Firm • Rapid growth• Well circumscribed • Fixed • Inflammation / edema • Ulceration • Pain
    14. 14. Physical Exam
    15. 15. Physical Exam
    16. 16. Physical Exam
    17. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 28. Veterinarian’s Oath
    29. 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. 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. 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. 32. EuthanasiaEvery 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. 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. 34. Questions?• Thank you!