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.

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.

Overview

A malignant tumor of vascular origin, classically attributed to endothelial cells, 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.

Overview

A malignant proliferation of cells within the mononuclear phagocyte/dendritic cell lineage. 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.

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.

Digital Melanoma

• Frequently malignant with early nodal and pulmonary metastasis; behaves similarly to oral melanoma.
• Immunohistochemistry for diagnosis when amelanotic: Melan-A, PNL2.
• Staging: regional node cytology/biopsy, thoracic imaging.
• Therapy: digit amputation; radiation for incomplete margins; immunotherapy considerations as for oral melanoma.

For oral melanoma, see the Oral Cavity section below.

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.

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.

Overview

A locally aggressive but non-metastasizing odontogenic tumor believed to arise from residual odontogenic epithelium, typically at the rostral mandible or maxilla. Exact histogenesis is not fully settled — proposed origins in the literature include epithelial rests of Malassez, remnants of the dental lamina, and basal cells of the gingival/oral mucosal epithelium. Historically termed "acanthomatous epulis," but CAA is the preferred and pathologically accurate designation, as this tumor is distinct from true epulides of periodontal ligament origin.

Clinical Behavior

• Locally invasive into bone; imaging typically shows lysis with tooth displacement or resorption, cortical thinning or expansion, and sometimes a multilocular "honeycomb" or "soap-bubble" pattern.
• Does not metastasize, but local recurrence is common with incomplete excision (e.g., curettage or marginal excision alone); recurrence is low with adequately wide margins.
• Rapid regrowth is characteristic if margins are insufficient.

Diagnosis

• Incisional or excisional biopsy with histopathology is required for definitive diagnosis; clinical appearance overlaps with other gingival masses.
• Advanced imaging (CT) is recommended pre-operatively to assess bony involvement and guide surgical margins.

Management

• Wide surgical excision (marginal or segmental mandibulectomy/maxillectomy) with approximately 2 cm bony margins is curative in most cases.
• Radiation therapy is an alternative for non-resectable lesions or when owners decline mandibulectomy, with good long-term control rates.

Overview

A benign, non-neoplastic proliferative lesion thought to arise from periodontal ligament fibrous tissue, presenting as a firm, well-differentiated gingival mass. FHGL is the preferred and pathologically accurate terminology over the traditional but imprecise designation "peripheral odontogenic fibroma (POF)," which implies an odontogenic epithelial origin not supported by the reactive/hyperplastic nature of this lesion.

Clinical Presentation

• Firm, smooth, pink, sessile or pedunculated mass arising from the gingival margin, most often at the periodontal ligament attachment of a single tooth.
• Slow-growing; does not ulcerate or bleed readily, distinguishing it clinically from more aggressive gingival masses.
• No significant bony lysis on imaging, in contrast to CAA or other odontogenic tumors.

Diagnosis

• Excisional biopsy with histopathology is recommended for definitive diagnosis, given clinical overlap with early CAA and other gingival proliferations.
• Histopathology shows a well-vascularized fibrous stroma with variable mineralization, without infiltrative odontogenic epithelial nests or malignant cytologic features.

Management

• Local surgical excision, including the periodontal ligament origin, is typically curative.
• Recurrence is uncommon with complete excision but can occur if the periodontal ligament attachment is incompletely removed.
• Does not require aggressive margins or bony resection, unlike CAA.

Overview

The most common malignant oral tumor in dogs, arising from mucosal melanocytes. Behavior differs markedly from cutaneous melanocytic tumors — oral melanoma is typically malignant with high metastatic potential, regardless of pigmentation.

Clinical Behavior

• Locally invasive with frequent bony involvement of the mandible or maxilla.
• High rate of regional lymph node and pulmonary metastasis at diagnosis.
• Amelanotic variants are not uncommon and can be mistaken for other spindle cell or epithelial tumors grossly and cytologically.

Diagnosis

• Histopathology remains the standard for diagnosis and grading (mitotic index, nuclear atypia, junctional activity).
• Immunohistochemistry (Melan-A, PNL2, or SOX10) is indicated for amelanotic or poorly differentiated tumors.
• Staging: regional lymph node cytology/biopsy (sentinel node evaluation where available) and thoracic imaging are recommended given high metastatic rates.

Prognosis and Management

• Mitotic index is one of the strongest prognostic factors; high mitotic count is associated with markedly shorter survival.
• Surgery (mandibulectomy/maxillectomy) with wide margins is first-line for resectable lesions.
• Radiation therapy provides good local control when margins are incomplete or surgery is not feasible.
• Adjunctive immunotherapy (melanoma vaccine) has been used, though survival benefit varies across studies.

Overview

A common malignant epithelial tumor of the oral cavity in dogs and cats. Biologic behavior varies substantially by site and species — tonsillar and lingual base SCC in dogs is far more aggressive than rostral (non-tonsillar) gingival SCC, and feline oral SCC carries a generally poor prognosis regardless of location.

Clinical Behavior

• Canine rostral/gingival SCC: Locally invasive with bony involvement but relatively low metastatic rate; can carry a favorable prognosis with aggressive local excision.
• Canine tonsillar/caudal tongue SCC: High metastatic potential to regional lymph nodes and lungs; prognosis guarded to poor.
• Feline oral SCC: Highly locally invasive, frequently involving mandible/maxilla or sublingual tissue; diagnosis is often made at an advanced, non-resectable stage.

Diagnosis

• Incisional biopsy with histopathology for definitive diagnosis and grading.
• CT is preferred over radiographs for assessing bony invasion and surgical planning.
• Regional lymph node cytology and thoracic imaging for staging, particularly in caudal oral or tonsillar lesions.

Management

• Surgical excision (mandibulectomy/maxillectomy) is the treatment of choice for resectable rostral lesions.
• Radiation therapy, often combined with surgery, is used for non-resectable or caudal lesions.
• Feline oral SCC has a poor overall response to most therapies; palliative care and early referral for feeding tube placement are often necessary given rapid impact on quality of life.

Overview

A benign, non-neoplastic proliferation of gingival fibrous connective tissue, most common in brachycephalic and large-breed dogs. Important to distinguish histologically from true odontogenic neoplasia (e.g., CAA, FHGL) and from reactive/inflammatory proliferations, as clinical appearance can overlap significantly.

Clinical Presentation

• Diffuse or focal gingival enlargement, often generalized around multiple teeth rather than a discrete mass.
• May be idiopathic or drug-associated (e.g., cyclosporine) in some patients.

Diagnosis

• Biopsy is recommended for any focal, rapidly growing, or ulcerated gingival enlargement to rule out neoplasia before assuming a benign hyperplastic process.
• Histopathology shows fibrous connective tissue proliferation with variable epithelial hyperplasia, without evidence of odontogenic epithelial nests or malignant features.

Management

• Gingivectomy/gingivoplasty for symptomatic or cosmetically significant lesions.
• Dental prophylaxis and periodontal management to reduce local inflammatory contribution.
• Recurrence is possible, particularly in predisposed breeds, and does not indicate malignant transformation.

Overview

A reaction pattern rather than a single disease entity, characterized by eosinophil-rich inflammation of the oral mucosa (commonly the upper lip, palate, or tongue). Often associated with underlying hypersensitivity (flea, food, environmental allergy) but can be idiopathic.

Clinical Presentation

• Indolent (rodent) ulcer: Well-demarcated ulcerative lesion, typically on the upper lip.
• Eosinophilic plaque: Raised, ulcerated, well-circumscribed lesion, often intensely pruritic.
• Linear granuloma: Raised, cobblestoned lesion, may affect the tongue, palate, or lips.

Diagnosis

• Cytology (impression smear or FNA) often shows abundant eosinophils and can be sufficient for a presumptive diagnosis in classic cases.
• Biopsy is recommended for atypical, non-responsive, or rapidly progressive lesions to exclude neoplasia (particularly oral SCC or mast cell tumor, which can mimic EGC lesions clinically).
• Histopathology shows eosinophilic and often collagenolytic/flame-figure inflammation.

Management

• Identification and management of underlying allergic trigger (flea control, elimination diet trial) is central to long-term control.
• Glucocorticoids or other anti-inflammatory/immunomodulatory therapy for acute lesions.
• Recurrence is common without addressing the underlying hypersensitivity.

Overview

An immune-mediated inflammatory condition characterized by painful ulceration where the buccal or lingual mucosa contacts the dental surface ("contact mucositis/ulceration"), thought to reflect a hypersensitivity reaction to plaque antigens ("kissing lesions").

Clinical Presentation

• Painful, often deep ulcers along the buccal mucosa opposing the maxillary/mandibular teeth, or lateral tongue margins.
• Halitosis, ptyalism, dysphagia, and reluctance to eat are common presenting complaints.

Diagnosis

• Primarily a clinical diagnosis based on lesion distribution and contact pattern with dental surfaces.
• Biopsy can be used to support the diagnosis and rule out other ulcerative or neoplastic oral disease, showing a lichenoid-to-ulcerative mucositis with a predominantly lymphoplasmacytic/plasmacytic infiltrate.

Management

• Meticulous dental care (professional cleaning, extraction of teeth in close contact with lesions) combined with strict home plaque control is the cornerstone of therapy.
• Immunomodulatory therapy (e.g., cyclosporine) is often needed for cases that do not resolve with dental management alone.
• Full-mouth or near-full-mouth extraction may be required for refractory, severely affected patients.

Overview

A severe, immune-mediated, proliferative and ulcerative inflammatory disease of the gingiva and caudal oral mucosa (caudal mucositis) in cats. Etiology is multifactorial, with proposed roles for chronic antigenic stimulation from plaque, feline calicivirus, and dysregulated immune response.

Clinical Presentation

• Severe, often symmetric inflammation and ulceration extending into the caudal oral mucosa/glossopalatine folds — a distribution pattern that helps distinguish FCGS from localized periodontal disease.
• Marked oral pain, halitosis, ptyalism, weight loss, and reluctance to eat or groom.

Diagnosis

• Primarily clinical, supported by the characteristic caudal mucositis distribution.
• Biopsy is useful in atypical presentations to exclude neoplasia (oral SCC in particular) and to characterize the inflammatory infiltrate (typically lymphoplasmacytic).
• Calicivirus PCR/testing may be pursued as part of the diagnostic workup, though its role in guiding therapy is limited.

Management

• Full-mouth or near-full-mouth tooth extraction is the treatment most consistently associated with clinical improvement or resolution.
• Adjunctive immunomodulatory therapy (e.g., cyclosporine) for cases with incomplete response to extractions.
• Refractory cases may require long-term multimodal pain management and immunosuppression.

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, with exceptions such as 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.

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

Overview

Mammary tumors are common in dogs and cats, but their biologic behavior differs markedly between species. Prognosis is influenced by tumor type, histologic grade, size, lymphatic invasion, and completeness of excision. Early surgical intervention is the most important modifiable prognostic factor.

Canine Mammary Tumors — General Behavior

Approximately 50% of canine mammary tumors are benign and 50% malignant. Dogs often develop multiple mammary nodules over time, which may represent independent tumors rather than metastasis.

• Benign: Adenomas, benign mixed mammary tumors, fibroadenomas. Surgical excision is typically curative; metastasis does not occur.
• Malignant: Mammary carcinomas (simple, complex, mixed), sarcomas, and inflammatory carcinoma (rare). Small, low-grade carcinomas (<3 cm) have favorable long-term outcomes; larger (>5 cm), high-grade, or lymphovascular-invasive tumors carry significantly higher metastatic risk.

Canine Grading, Prognostic Indicators & Surgical Considerations

• Histologic grading (I–III) assesses differentiation, mitotic activity, and invasiveness.
• Ki-67 and mitotic index may provide additional prognostic refinement in malignant tumors.
• Lymph node involvement worsens prognosis.
• Margins are critical; complete excision improves survival. Ovariohysterectomy at the time of tumor removal may reduce risk of future tumors if performed early in life, but has limited impact once tumors are present.

Feline Mammary Tumors — General Behavior

In contrast to dogs, 85–95% of feline mammary tumors are malignant, and they are typically aggressive carcinomas with early metastatic potential.

• Most are adenocarcinomas.
• Tumor size is a strong prognostic factor: <2 cm has significantly longer survival; 2–3 cm intermediate prognosis; >3 cm poor prognosis with high metastatic risk.

Feline Grading, Prognostic Indicators & Management

• Histologic grade strongly correlates with outcome. High-grade tumors, lymphatic invasion, and high Ki-67 indices are associated with shorter survival times.
• Metastasis commonly involves regional lymph nodes and lungs.
• Radical mastectomy (unilateral or bilateral staged procedures) provides better local control than lumpectomy. Adjuvant chemotherapy may improve disease-free intervals in select cases.

Prevention

Early ovariohysterectomy dramatically reduces risk of mammary tumor development in both dogs and cats.

Prognosis Summary

• Dogs: Prognosis ranges from excellent (benign or low-grade malignant tumors) to guarded (high-grade carcinomas).
• Cats: Prognosis is often guarded to poor, particularly for large or high-grade tumors; early detection is critical.