Incomplete Margins: Indicate possible local recurrence; re-excision or radiation often warranted.

Staging Importance: Advanced imaging and lymph node evaluation refine prognosis and guide therapy in aggressive or high-grade tumors.

Adjuvant Therapy: Radiation or chemotherapy should be considered for incompletely excised, high-grade, or metastatic lesions.

Overview

Canine mast cell tumors show wide variation in behavior. Prognosis depends on histologic grade, proliferative activity, molecular profile, and completeness of excision.

Grading and Prognosis

Two grading systems are widely used: Patnaik (Grades I–III) and Kiupel (Low vs. High grade). Low-grade tumors tend to have prolonged survival with complete excision, while high-grade lesions often metastasize or recur quickly. Mitotic index and presence of vascular or lymphatic invasion strongly influence prognosis.

Margins and Local Control

Histologic margin assessment is crucial. Tumor-free margins (>2 mm) correlate with reduced recurrence; incomplete margins may justify re-excision or radiation therapy.

Molecular and Proliferation Testing

• KIT (CD117) Pattern: Membranous staining indicates favorable behavior; diffuse cytoplasmic patterns correlate with aggressive biology and c-KIT mutation.

• Ki-67 / AgNOR: Quantify proliferation rate; higher values predict shorter survival.

• c-KIT PCR Mutation Testing: Detects activating mutations (usually exon 11 ITDs). Indicated for high-grade, recurrent, or multifocal MCTs, or when considering tyrosine kinase inhibitor (TKI) therapy. Mutation-positive tumors are more likely to respond to TKIs but carry a worse prognosis.

Prognostic Panels

Commercial panels combining grade, proliferation markers, KIT pattern, and c-KIT PCR improve risk stratification and guide therapeutic decisions.

Staging and Therapy

Stage via regional node cytology, abdominal ultrasound (liver/spleen), and thoracic imaging. - Surgery is primary treatment; adjuvant radiation or systemic therapy (vinblastine, lomustine, TKIs) considered for high-risk cases.

References

- Withrow & MacEwen’s Small Animal Clinical Oncology, latest ed.
- Kiupel M. et al. Two-tier grading for canine cutaneous mast cell tumors. Vet Pathol. 2011.
- Patnaik AK. et al. Canine cutaneous mast cell tumors: morphologic grading and survival. Vet Pathol. 1984.
- Romansik EM. et al. KIT pattern and prognosis in canine MCT. Vet Pathol. 2007.
- Webster JD. et al. c-KIT mutations in canine MCT. Vet Pathol. 2006.

Overview

Feline MCTs occur in cutaneous or visceral forms (spleen, intestine). Cutaneous MCTs are typically benign; visceral variants may be systemic and aggressive.

Cutaneous Form

• Common in older cats; usually cured by complete excision.

• Recurrence is rare; metastasis uncommon.

Visceral Forms

• Splenic MCT: Splenectomy often results in long remission, though marrow/hepatic spread may occur.

• Intestinal MCT: Generally poorer prognosis; metastatic spread is common.

Prognostic Testing

Proliferation indices (e.g., Ki-67) and mitotic rate can aid risk assessment in splenic cases. c-KIT mutations are less frequent than in dogs but may occur in aggressive variants.

References

- Withrow & MacEwen’s Small Animal Clinical Oncology, latest ed.
- Sabattini S., Bettini G. Prognosis of feline splenic MCT. J Feline Med Surg. 2010+.
- Blackwood L. et al. ESVONC/ACVIM guidance on feline MCT (consensus/position statements).

Overview

Lymphoma comprises diverse lymphoid neoplasms varying by anatomic distribution and immunophenotype (B-cell, T-cell). Prognosis and treatment are driven by phenotype, grade, and stage.

Phenotyping — Flow Cytometry & IHC (CD3, Pax5)

• Flow cytometry: On fine-needle aspirates or effusions, rapidly distinguishes B vs. T lineage and provides information on size (FSC/SSC), antigen density, and co-expression patterns that suggest aggressive biology. Useful for staging (blood/bone marrow) without anesthesia.

• IHC on biopsies/cytology cell blocks:

• CD3 confirms T-cell lineage. T-cell lymphomas often have shorter remission durations (exceptions exist, e.g., nasal B-cell in cats).

• PAX5 (BSAP) is a nuclear B-cell marker that remains positive through most stages of B-cell differentiation; helpful when CD79a/CD20 are equivocal or antigen expression is lost after therapy.

• How to use together: Start with flow cytometry when cellular yield allows; add IHC (CD3, PAX5 ± CD20/ CD79a) for architectural context or when flow is inconclusive.

Clonality — PARR (PCR for Antigen Receptor Rearrangement)

Why: Distinguishes clonal (neoplastic) lymphoid populations from reactive hyperplasia when cytology/ histology is equivocal; detects minimal residual disease in follow-up; resolves discordant flow/IHC results.

When

• Small round-cell infiltrates where cytology suggests lymphoma but inflammation is possible (e.g., felineGI).

• Cutaneous lymphoma vs. severe dermatitis; nodal hyperplasia vs. early lymphoma.

• Post-treatment monitoring when determining relapse vs. rebound hyperplasia.

• Caveats: False negatives if tumor burden is low or primer sets don’t match rearrangement; false positives can occur in very restricted reactive responses—interpret alongside clinical and path findings.

Staging (WHO-based, species-adapted)

• Minimum database: CBC/chemistry/UA.

• Imaging: Thoracic radiographs or CT; abdominal ultrasound for liver/spleen/mesenteric nodes; consider nasal/skull imaging in cats with upper respiratory signs.

• Sampling: Aspirate or core biopsy of enlarged nodes; bone marrow aspirate for high-grade or cytopenic cases; flow cytometry on blood/marrow to quantify circulating burden.

• Additional tests: FeLV/FIV in cats; Ca++ monitoring in T-cell and mediastinal forms; echocardiography if doxorubicin is anticipated.

• Stage-to-treatment link: High tumor burden or extranodal organ involvement often favors multi-agent chemo (e.g., CHOP). Low-grade feline GI lymphoma may be managed with chlorambucil/pred.

Prognosis (selected patterns)

• Canine multicentric B-cell: Median survival ~8–12 months with CHOP; CR rates 60–90% initially.-

• Canine T-cell: Shorter remission ("T- for terrible" heuristic, with exceptions).

• Feline alimentary low-grade (T-cell): Indolent course; months–years with chlorambucil/pred.-

• Feline nasal (often B-cell): Good local control with radiation ± chemo.

References

- Valli VE. et al. Veterinary Comparative Hematopathology; WHO classification adaptations.
- Avery AC. et al. Flow cytometry in canine lymphoma. Vet Clin Pathol / Vet J reviews.
- Burnett RC. et al. PARR for clonality in canine/feline lymphoma. Vet Pathol. 2003+.
- ACVIM Consensus Statements on lymphoma diagnosis/staging (latest).
- Withrow & MacEwen’s Small Animal Clinical Oncology, latest ed.

Overview

A malignant proliferation of interstitial dendritic cells or macrophages. Occurs in localized (periarticular, soft tissue, pulmonary) and disseminated forms. Predisposed breeds include Bernese Mountain Dogs, Rottweilers, and Retrievers.

Clinical Behavior

• Localized forms often occur in joints, spleen, or skin; may remain regional initially.

• Disseminated histiocytic sarcoma (malignant histiocytosis) presents with rapid multi-organ involvement.

Key Diagnostics

• Immunophenotyping (e.g., CD18, Iba-1, CD204) to confirm histiocytic lineage and exclude mimics (lymphoma, undifferentiated sarcoma).

• Advanced imaging (CT) for staging and surgical planning.

Prognosis and Therapy

Highly aggressive; survival often <6 months without intervention. Localized lesions may benefit from surgical excision and lomustine-based chemotherapy; palliative RT can improve comfort. Disseminated disease carries poor prognosis despite therapy.

References

- Moore PF., Affolter VK. Histiocytic diseases of dogs. Vet Pathol. Reviews.
- Skorupski KA. et al. Outcome with lomustine in canine histiocytic sarcoma. J Vet Intern Med.
- Withrow & MacEwen’s Small Animal Clinical Oncology, latest ed.

Overview

Melanocytic tumors may be benign or malignant, arising in skin, oral cavity, or digits. Behavior depends strongly on location and malignancy grade.

Cutaneous (haired skin)

• Often benign; excision typically curative.

• Monitor for atypical features or recurrence.

Oral and Digital Melanoma

• Frequently malignant with early nodal and pulmonary metastasis.

• Immunohistochemistry for diagnosis when amelanotic: Melan-A, PNL2.

• Staging: Regional node cytology/biopsy (including sentinel node mapping where available), thoracic imaging, and +/- abdominal imaging.

Therapy & Prognosis

• Surgery: Wide excision or mandibulectomy/maxillectomy for oral lesions; digit amputation for digital lesions.

• Radiation: Useful for local control when margins are incomplete or in non-resectable sites.

• Immunotherapy: Tyrosinase DNA vaccine has been used as adjunctive therapy; survival benefit varies across studies.

References

- Smith SH., Goldschmidt MH., McManus PM. Canine melanocytic neoplasms. Vet Pathol.
- Bergman PJ. et al. Tyrosinase DNA vaccine experiences in canine melanoma.
- Withrow & MacEwen’s Small Animal Clinical Oncology, latest ed.

Overview

A malignant tumor of endothelial origin with variable presentation and prognosis depending on anatomic location. High metastatic potential, particularly for visceral and cardiac forms.

Cutaneous Form

• Often UV-induced in lightly pigmented, sparsely haired dogs.

• Generally superficial and may be cured with complete excision.

• Deep dermal or subcutaneous extension worsens prognosis.

Subcutaneous Form

• More aggressive than dermal-only; approximately 30–50% metastasize.

• Metastatic sites: lungs, liver, spleen.

Splenic Hemangiosarcoma

• Most common visceral form; presents with hemoabdomen, collapse, or anemia.

• High metastatic rate (up to 80%).

• Splenectomy followed by chemotherapy (doxorubicin-based) may extend survival to ~4–6 months median.

Right Atrial (Cardiac) Hemangiosarcoma

• Typically arises from right auricular appendage.

• Commonly results in pericardial effusion/tamponade.

• Prognosis poor: median survival ~1–3 months with surgery alone, 4–6 months with adjunctive chemo.

Ancillary Diagnostics

• Thoracic imaging for pulmonary metastasis.

• Abdominal ultrasound or CT for concurrent splenic/liver lesions.

• CBC: regenerative anemia, schistocytes, acanthocytes.

References

- Brown NO. et al. Hemangiosarcoma in the dog: retrospective studies. J Am Vet Med Assoc.
- Sorenmo KU. Hemangiosarcoma: biology, diagnosis, and management. Clin Tech Small Anim Pract.
- Withrow & MacEwen’s Small Animal Clinical Oncology, latest ed.

Overview

Chronic UV radiation causes actinic injury leading to neoplastic transformation in lightly pigmented or sparsely haired animals, especially cats and dogs with white fur.

Common Tumor Types

• Squamous Cell Carcinoma: Most frequent; arises on pinnae, nasal planum, eyelids.

• Hemangioma/Hemangiosarcoma: UV-induced variants common on ventral abdomen and inguinal skin.

• Basal Cell Carcinoma and Actinic Keratosis: Represent pre-neoplastic and early neoplastic changes.

Prevention and Management

• Limit UV exposure, provide shade, and use protective clothing or sunscreen for high-risk animals.

• Early excision of actinic keratoses prevents malignant transformation.

• Radiation therapy or photodynamic therapy may be considered for small lesions.

Prognosis

Dependent on the depth of invasion and early detection; superficial lesions carry an excellent prognosis.

References

- Scott DW. et al. Solar-induced skin disease in animals. Vet Dermatol reviews.
- Goldschmidt MH., Hendrick MJ. Tumors of the Skin and Soft Tissues.
- Withrow & MacEwen’s Small Animal Clinical Oncology, latest ed.

Overview

A malignant epithelial tumor of the subungual/nailbed epithelium, common in middle-aged to older dogs (over-represented in black-coated breeds).

Clinical Presentation

Chronic nail loss, swelling, bleeding, or lameness; often mistaken for infection/trauma.

Behavior and Prognosis

Locally invasive with moderate metastatic potential to regional lymph nodes; pulmonary spread occurs later.

Management

• Digit amputation is typically curative in non-metastatic cases.

• Stage with regional node evaluation and thoracic imaging.

References

- Henry CJ., et al. Digital SCC in the dog: presentation and outcome. J Am Vet Med Assoc / Vet Comp Oncol.
- Withrow & MacEwen’s Small Animal Clinical Oncology, latest ed.