RA

Veterinary Oncology – Core Vocabulary

Historical Context & Significance of Veterinary Oncology

  • Earliest recorded cancer case: Edwin Smith papyrus (Ancient Egypt).
  • S. Mukherjee’s book “Emperor of All Maladies” – parallels human & canine cancer history.
  • Increase in canine cancer incidence linked to:
    • Extended pet longevity due to improved care.
    • Heightened owner awareness & willingness to diagnose/treat.
  • Human oncology heavily influences veterinary protocols (chemotherapy, radiation).
  • Cancer therapy = balance of efficacy, cost, stress & quality-of-life (QOL).

Epidemiology & General Risk Factors

  • Estimated ≥50 % of canine deaths after age \ge10 due to cancer.
  • Veterinarian’s front-line roles: screening, offering options, client education.
  • Major risk determinants:
    • Age: incidence rises with age; some tumors show bimodal peaks (e.g., osteosarcoma in juvenile & middle-aged giants).
    • Breed predispositions (examples):
    • Golden Retrievers & Boxers – lymphoma.
    • Irish Wolfhounds, Greyhounds – osteosarcoma.
    • German Shepherds – hemangiosarcoma.
    • Bassets – trichoepithelioma.
    • Sex: males – perianal gland tumors; females – mammary tumors.
    • Environment: urban pollution → tonsillar/upper-airway carcinoma; owner smoking correlates with bladder TCC.

Metastasis Fundamentals

  • Primary tumor rarely lethal; metastasis causes death.
  • Common fatal site: lungs.
  • Route mechanics:
    1. Angiogenesis around primary mass.
    2. Tumor cell detachment & intravasation.
    3. Circulatory survival (immune evasion).
    4. Vascular arrest at distant capillary bed.
    5. Extravasation & colonization.
  • Spread via lymphatics, vasculature, or direct seeding/rupture (e.g., splenic hemangiosarcoma).

Clinical Approach: Initial Work-Up

  • Step 1 – Detailed history (onset, progression, husbandry, diet, vax, comorbid pets).
  • Step 2 – Thorough physical exam
    • Palpate all peripheral LNs, oral cavity, thorax auscultation, abdominal palpation.
    • Add orthopaedic/neurologic/ophthalmic exams as indicated.
  • Minimum database for any geriatric/suspect case:
    • CBC, serum chemistry, UA ± urine culture.
    • Thoracic radiographs (3-view) – pulmonary mets.
    • Abdominal ultrasound (under-utilised yet invaluable).
  • Tissue sampling hierarchy:
    • Fine-needle aspirate (FNA) → cytology (screening, not definitive).
    • Biopsy (punch, wedge, excisional) → histopathology = gold standard.
  • Advanced imaging / tests when indicated: CT, MRI, bone scan (^{99m}\text{Tc}), bone-marrow aspirate.
  • Principle: the more complete the staging, the clearer the prognosis & treatment roadmap.

Cancer Staging Concept

  • Non-uniform; tumour-specific numeric scales (commonly 1\text{–}5).
  • Guides prognosis, cost, and aggressiveness of therapy.
  • Example: Lymphoma staging (plus sub-stages a/b)
    • I = single LN.
    • II = multiple nodes, same side of diaphragm.
    • III = generalized LN involvement.
    • IV = III + liver/spleen.
    • V = IV + blood/bone-marrow involvement.
    • Sub-stage a = no systemic signs; b = systemic illness.

Treatment Modalities

Chemotherapy

  • Systemic; best for disseminated disease.
  • Modes: anti-metabolites (false substrates) vs alkylating agents (DNA cross-link).
  • High-growth-fraction tumours ⇒ more chemosensitive.
  • Toxicity–efficacy balancing: maintain therapeutic plasma levels without intolerable side-effects (GI upset, myelosuppression, mild alopecia).
  • Resistance inevitable → combination therapy (multiple drugs) & multimodal therapy (chemo + surgery/radiation/etc.).

Radiation Therapy (XRT / DXT)

  • Localised ionising beam (e.g., linear accelerator).
  • Uses: curative, adjunctive, or palliative (tumour debulking to relieve pain/obstruction).
  • Radiosensitivity hierarchy: haematopoietic > epithelial > mesenchymal.
  • Tumour response linked to growth fraction & oxygenation (hypoxic cells radio-resistant).
  • Toxicities: local dermatitis/alopecia, mucositis, N/V/D.

Ancillary / Tumour-Specific Options

  • Surgery (e.g., limb amputation, mastectomy).
  • Diet modifications, weight loss, supplements.
  • Empirical antibiotics, analgesia.
  • Palliative care emphasising QOL.

Top 10 Canine Tumours (8 malignant + 2 benign)

1. Lymphoma

  • Breeds: Golden, Boxer.
  • B-cell (better) vs T-cell (terrible).
  • Clinical forms: multicentric (LN), mediastinal, GI, cutaneous, etc.
  • Dx: CBC/chem, thoracic rads, abdominal U/S, FNA + biopsy, +/- hypercalcaemia (paraneoplastic).
  • Tx: CHOP-based chemo; prognosis 2\text{ mo} \to 3\text{ yr} (stage-dependent).

2. Multiple Myeloma

  • Systemic malignant plasma-cell tumour; osteolytic axial lesions.
  • Hallmarks (need ≥2):
    • Monoclonal gammopathy (IgG/IgA) = paraproteinaemia.
    • >10\% neoplastic cells in marrow.
    • Benz-Jones proteinuria.
    • Osteolytic bone lesions.
  • Tx: prednisone + melphalan (Leukeran); palliative radiation for painful foci.
  • MST ≈ 18\text{ mo}.

3. Leukaemias

Chronic Lymphocytic Leukaemia (CLL)

  • Older dogs; mature lymphocytosis; deaths due to infections.
  • Tx: Leukeran ± prednisone.

Acute Lymphoblastic Leukaemia (ALL)

  • Young Labs; blasts in marrow, anaemia/thrombocytopaenia common; rapid fatality even with chemo (weeks–months).

4. Mammary Tumours

  • 42\% of intact bitches’ tumours.
  • Malignant : benign ≈ 1:1 (mixed histology common).
  • OHE before 1st heat ⇒ risk 0.5\%; after 1 heat ⇒ 8\%; rises with each cycle.
  • Caudal abdominal & inguinal glands most affected; LN drainage (inguinal/axillary) critical.
  • Tx: wide surgical excision (entire chain if multiple), ± chemo/radiation; beware implantation seeding.

5. Mast-Cell Tumours (MCT)

  • “Think of the B breeds”: Boxers, Bostons, Bulldogs.
  • Dermal (firm/nodular) vs sub-Q (flaccid/ill-defined).
  • Produce histamine & heparin → GI ulcers, coagulopathy.
  • Dx: FNA cytology; stage via abdomen imaging.
  • Tx: wide surgery + antihistamines (+/- chemo, RT).

6. Soft-Tissue Sarcoma (incl. Feline Vaccine-Associated Sarcoma)

  • Dogs: less common but behave invasively, poor margins.
  • Cats: classic aggressive sub-Q mass at vax sites → tail/distal-limb injections recommended.
  • Tx: radical surgery (>3 cm margins) + RT.

7. Osteosarcoma

  • Giant breeds; bimodal age (18 mo & 5–8 yr).
  • Predilection: distal radius > other long-bone metaphyses.
  • Fast primary growth; pulmonary mets often occult at dx, become evident within months.
  • Tx: limb amputation ± chemo ± palliative RT.
  • MST ≈ 1\text{ yr} (longer with aggressive multimodal protocol).

8. Hemangiosarcoma

  • Older German Shepherds.
  • Origin: vascular endothelium (spleen >> heart, skin).
  • Classic presentation: acute collapse from splenic rupture → auto-transfuse & transient recovery.
  • Dx: FAST ultrasound, abdominocentesis, rads.
  • Tx: splenectomy ± doxorubicin-based chemo; survival ranges months–years.

9. Transitional Cell Carcinoma (Bladder) – Benign-LOOK-ALIKE DIFFERENTIAL but actually malignant

  • Mid-old females, obese, Shelties & Scotties high-risk; passive smoke link.
  • Location: trigone (U/S image = echogenic “sludge” in funnel).
  • Recurrent refractory “UTI” red flag.
  • Never aspirate transabdominally (needle-track seeding).
  • Mets common at dx.
  • Tx: partial cystectomy, NSAIDs (piroxicam), RT/chemo; risk of post-RT incontinence.

10. Benign Tumours

a) Lipoma

  • Older, overweight females (Labs, Dobies, Schnauzers).
  • Soft, mobile sub-Q masses; monitor size/location.
  • Excise if impairing gait or rapidly enlarging (rule-out liposarcoma).

b) Trichoepithelioma (Hair-Follicle Tumour)

  • Basset Hounds poster child.
  • Small pedunculated/cystic dermal nodules; pruritic → self-trauma/infection.
  • Surgical removal curative yet may induce satellites; weigh risk vs benefit.

Ethical / Practical Take-Aways

  • ALWAYS centre decision-making on QOL, not tumour eradication alone.
  • Transparent dialog on cost, prognosis, side-effects empowers owners.
  • Client education on breed risks & early spay/neuter = primary prevention.
  • Diagnostic diligence (U/S, rads, cytology) prevents misdiagnosis & delays.
  • Remember: “Cancer doesn’t kill; metastasis does.”