Pathology in Practice

Melinda S. Camus from the Departments of Pathology (Camus, Brooker, Howerth, Seguel), Veterinary Biosciences and Diagnostic Imaging (Perlini, Secrest), and Small Animal Medicine (Feldhaeusser, Saba), College of Veterinary Medicine, University of Georgia, Athens, GA 30602.

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Alyssa Brooker from the Departments of Pathology (Camus, Brooker, Howerth, Seguel), Veterinary Biosciences and Diagnostic Imaging (Perlini, Secrest), and Small Animal Medicine (Feldhaeusser, Saba), College of Veterinary Medicine, University of Georgia, Athens, GA 30602.

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Michael Perlini from the Departments of Pathology (Camus, Brooker, Howerth, Seguel), Veterinary Biosciences and Diagnostic Imaging (Perlini, Secrest), and Small Animal Medicine (Feldhaeusser, Saba), College of Veterinary Medicine, University of Georgia, Athens, GA 30602.

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Scott Secrest from the Departments of Pathology (Camus, Brooker, Howerth, Seguel), Veterinary Biosciences and Diagnostic Imaging (Perlini, Secrest), and Small Animal Medicine (Feldhaeusser, Saba), College of Veterinary Medicine, University of Georgia, Athens, GA 30602.

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Elizabeth W. Howerth from the Departments of Pathology (Camus, Brooker, Howerth, Seguel), Veterinary Biosciences and Diagnostic Imaging (Perlini, Secrest), and Small Animal Medicine (Feldhaeusser, Saba), College of Veterinary Medicine, University of Georgia, Athens, GA 30602.

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Mauricio Seguel from the Departments of Pathology (Camus, Brooker, Howerth, Seguel), Veterinary Biosciences and Diagnostic Imaging (Perlini, Secrest), and Small Animal Medicine (Feldhaeusser, Saba), College of Veterinary Medicine, University of Georgia, Athens, GA 30602.

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Brittany Feldhaeusser from the Departments of Pathology (Camus, Brooker, Howerth, Seguel), Veterinary Biosciences and Diagnostic Imaging (Perlini, Secrest), and Small Animal Medicine (Feldhaeusser, Saba), College of Veterinary Medicine, University of Georgia, Athens, GA 30602.

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Corey Saba from the Departments of Pathology (Camus, Brooker, Howerth, Seguel), Veterinary Biosciences and Diagnostic Imaging (Perlini, Secrest), and Small Animal Medicine (Feldhaeusser, Saba), College of Veterinary Medicine, University of Georgia, Athens, GA 30602.

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History

A 15-year-old 22.1-kg neutered male German Shorthaired Pointer was presented for evaluation of weight loss and bloody diarrhea of approximately 1 month’s duration. The diarrhea resolved with administration of metronidazole but recurred with cessation of treatment.

Clinical and Clinicopathologic Findings

Hematologic findings were largely unremarkable. However, serum biochemical analysis revealed mild elevations in BUN concentration (43 mg/dL; reference interval, 9 to 31 mg/dL), alanine aminotransferase activity (376 U/L; reference interval, 18 to 121 U/L), and alkaline phosphatase activity (202 U/L; reference interval, 5 to 160 U/L). Abdominal ultrasonography revealed a 1.4-cm-diameter targetoid lesion in the left lateral liver lobe and a 2.5-cm-diameter heterogeneous mass, which was suspected to be a lymph node, in the cranial portion of the abdomen between the stomach and the transverse colon and adjacent to the splenic vein. Fine-needle aspirate specimens were obtained from both the liver nodule (Figure 1) and the mass.

Figure 1
Figure 1

Photomicrograph of a fine-needle aspirate specimen obtained from the liver of a 15-year-old German Shorthaired Pointer with weight loss and bloody diarrhea. There are scattered round to stellate cells with variable amounts of intracytoplasmic blue-black pigment surrounding a single round to ovoid nucleus with variable numbers of nuclei. A focal aggregate of well-differentiated hepatocytes is noted. Modified Wright stain; bar = 10 µm. Inset—Individualized round to stellate cells each have a single round nucleus and 1 or 2 variably sized nucleoli. Modified Wright stain; bar = 10 µm.

Citation: Journal of the American Veterinary Medical Association 259, 7; 10.2460/javma.259.7.741

The liver nodule aspirate specimen was moderately cellular with marked hemodilution and blood-associated leukocytes. The background was lightly basophilic and contained a moderate amount of granular, green-black extracellular pigment. Low numbers of hepatocytes, including occasional binucleated hepatocytes, were noted. There were many individualized, round to spindle-shaped cells (maximum dimension, approx 10 to 15 µm). Each cell contained a moderate amount of lightly eosinophilic cytoplasm that was filled with abundant small, green-black pigment granules, similar to those seen in the background, and a round to oval nucleus with lightly stippled chromatin and occasionally 1 or 2 prominent nucleoli. In this cell population, anisocytosis and anisokaryosis were moderate to marked and binucleation was rare.

Additional Cytologic Findings

Fine-needle aspirate specimens of the cranial abdominal mass yielded a similar population of pleomorphic, pigmented mesenchymal cells and no cytologic evidence of lymph node tissue, suggesting complete effacement of the node by a neoplastic cell population. Thoracic imaging performed after specimen collection revealed multifocal pulmonary masses with possible middle tracheobronchial lymphadenomegaly, consistent with metastatic neoplasia.

This dog had a history of a malignant gingival melanoma that was incompletely excised 5 years earlier. The gingival melanoma was 0.5 × 0.3 × 0.2 cm and located on the buccal side of the mandibular gingiva. Histologically, it was highly cellular, poorly circumscribed, and infiltrative and composed of cords of polygonal and spindle-shaped cells supported by fine fibrovascular stroma (Figure 2). Individual cells had variably distinct cell borders and a moderate amount of eosinophilic cytoplasm that contained a moderate amount of dark-brown granular pigment (melanin) and a round to oval nucleus that contained ≤ 2 magenta nucleoli. The mitotic rate was 1/10 hpf (400×; equivalent to 0.5 mm2), and anisocytosis and anisokaryosis were mild. There was no evidence of vascular or lymphatic invasion, although tumor cells extended to 1 edge of the sections. Scar revision was performed approximately 1 month after surgery and revealed no evidence for disease.

Figure 2
Figure 2

Photomicrograph of a section of a gingival mass in the dog in Figure 1 that was incompletely excised 5 years earlier. The mass is a highly cellular, poorly circumscribed, and infiltrative neoplasm, composed of cords of polygonal and spindle-shaped cells supported by fine fibrovascular stroma. H&E stain; bar = 200 µm. Inset—Neoplastic cells extend to the epithelium–lamina propria junction. Individual spindle-shaped neoplastic cells each have variably distinct cell borders and a moderate amount of eosinophilic cytoplasm that contains a moderate amount of dark-brown granular pigment (melanin) and a round to oval nucleus with ≤ 2 magenta nucleoli. H&E stain; bar = 30 µm.

Citation: Journal of the American Veterinary Medical Association 259, 7; 10.2460/javma.259.7.741

Morphologic Diagnosis and Case Summary

Morphologic diagnosis and case summary: cytologic evidence of intrahepatic melanoma and presumptive metastasis to the intra-abdominal lymph nodes and lungs.

Comments

Melanomas are composed of neoplastic melanocytes that originate in the neuroectoderm. These tumors are the most common malignant neoplasm in the oral cavity of dogs, and melanomas originating in the oral cavity are typically more biologically aggressive than cutaneous melanomas. Among dogs, there is no sex or well-established breed predisposition for development of oral melanomas, and the mean age of dogs with malignant oral melanomas at the time of diagnosis is 12 years.1,2

The cytologic and histologic diagnosis of poorly pigmented melanomas can be a diagnostic challenge requiring the use of special stains or immunohistochemical analysis. However, the diagnosis of well-pigmented melanomas is relatively straightforward when morphological features are not obscured by the presence of abundant pigment granules. Bleaching of pigment granules with 1% potassium permanganate may facilitate microscopic examination.1 A mitotic index should be determined for the area with the highest mitotic rate in histologic sections because the mitotic index has strong prognostic relevance. Among dogs with melanoma, approximately 80% of those that have ≥ 4 mitoses/10 hpf live less than a year after diagnosis, whereas only 10% of those with < 4 mitoses/10 hpf die within that time frame.1 In addition to the mitotic index, the degree of nuclear atypia and the Ki67 (growth fraction marker) labeling index have proven useful in distinguishing biologically aggressive melanomas from less aggressive melanomas. The degree of ulceration, inflammation, necrosis, and junctional activity have less prognostic importance.1

Clinical prognosis for dogs with melanoma is primarily determined by use of the World Health Organization staging system, which considers the primary tumor size and the presence of local or distant metastasis (or both) as the basis for assigning a tumor stage from I through IV, with high stages correlating to decreased survival time.3 Approximately 50% of oral melanomas metastasize to distant rather than mandibular lymph nodes.4 At least two-thirds of malignant melanomas spread to distant sites, most commonly the lungs; radiographically, pulmonary metastases typically have a miliary or nodular pattern, which makes them difficult to detect with that diagnostic imaging technique.1

Surgical excision remains the treatment of choice for oral malignant melanomas. However, newer, less invasive treatments are becoming available. A DNA-based vaccinea (xenogeneic immunotherapy) has been approved by the USDA as an adjunct treatment in dogs with malignant melanoma. The vaccine contains human tyrosinase genes that induce antibody and cytotoxic T-cell responses, with the goal of tumor rejection and extended survival time for affected dogs. It is administered transdermally, with minimal adverse effects, biweekly for 4 doses initially and then every 6 months thereafter. Information regarding the vaccine’s efficacy is limited and has been equivocal.5 More recently, investigation of immune checkpoint inhibitors has begun because of reported success of their use in human melanoma cases. These monoclonal antibodies bind ligands, such as CTLA-4 and PD-1, on T-lymphocytes and are intended to interfere with the regulatory mechanisms of the tumor microenvironment, resulting in prolonged T-cell activation and ultimately tumor regression. The compounds may also be promising for other cancers because they are not tumor specific.6

The dog of the present report received no additional treatment for the melanoma beyond margin revision following the initial tumor removal. Once liver metastasis was detected, the dog was administered prednisone (15 mg, PO, q 24 h) to improve its quality of life until the time of euthanasia.

Footnotes

a.

Boehringer Ingelheim, Duluth, Ga.

References

  • 1.

    Munday JS, Löhr CV, Kiupel M, et al. Tumors of the alimentary tract. In: Meuten DJ, ed. Tumors in domestic animals. 5th ed. Ames, Iowa: Wiley Blackwell, 2017;515524.

    • Search Google Scholar
    • Export Citation
  • 2.

    Ramos-Vara JA, Beissenherz ME, Miller MA, et al. Retrospective study of 338 canine oral melanomas with clinical, histologic, and immunohistochemical review of 129 cases. Vet Pathol 2000;37:597608.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 3.

    Bergman PJ, Kent MS, Farese JP. Melanoma. In: Withrow SJ, Vail DM, Page RL, eds. Withrow and MacEwen’s small animal clinical oncology. 5th ed. St Louis: Elsevier Saunders, 2013;321334.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 4.

    Herring ES, Smith MM, Robertson JL. Lymph node staging of oral and maxillofacial neoplasms in 31 dogs and cats. J Vet Dent 2002;19:122126.

  • 5.

    Grosenbaugh DA, Leard AT, Bergman PJ, et al. Safety and efficacy of a xenogeneic DNA vaccine encoding for human tyrosinase as adjunctive treatment for oral malignant melanoma in dogs following surgical excision of the primary tumor. Am J Vet Res 2011;72:16311638.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 6.

    Regan D, Guth A, Coy J, et al. Cancer immunotherapy in veterinary medicine: current options and new developments. Vet J 2016;207:2028.

  • Figure 1

    Photomicrograph of a fine-needle aspirate specimen obtained from the liver of a 15-year-old German Shorthaired Pointer with weight loss and bloody diarrhea. There are scattered round to stellate cells with variable amounts of intracytoplasmic blue-black pigment surrounding a single round to ovoid nucleus with variable numbers of nuclei. A focal aggregate of well-differentiated hepatocytes is noted. Modified Wright stain; bar = 10 µm. Inset—Individualized round to stellate cells each have a single round nucleus and 1 or 2 variably sized nucleoli. Modified Wright stain; bar = 10 µm.

  • Figure 2

    Photomicrograph of a section of a gingival mass in the dog in Figure 1 that was incompletely excised 5 years earlier. The mass is a highly cellular, poorly circumscribed, and infiltrative neoplasm, composed of cords of polygonal and spindle-shaped cells supported by fine fibrovascular stroma. H&E stain; bar = 200 µm. Inset—Neoplastic cells extend to the epithelium–lamina propria junction. Individual spindle-shaped neoplastic cells each have variably distinct cell borders and a moderate amount of eosinophilic cytoplasm that contains a moderate amount of dark-brown granular pigment (melanin) and a round to oval nucleus with ≤ 2 magenta nucleoli. H&E stain; bar = 30 µm.

  • 1.

    Munday JS, Löhr CV, Kiupel M, et al. Tumors of the alimentary tract. In: Meuten DJ, ed. Tumors in domestic animals. 5th ed. Ames, Iowa: Wiley Blackwell, 2017;515524.

    • Search Google Scholar
    • Export Citation
  • 2.

    Ramos-Vara JA, Beissenherz ME, Miller MA, et al. Retrospective study of 338 canine oral melanomas with clinical, histologic, and immunohistochemical review of 129 cases. Vet Pathol 2000;37:597608.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 3.

    Bergman PJ, Kent MS, Farese JP. Melanoma. In: Withrow SJ, Vail DM, Page RL, eds. Withrow and MacEwen’s small animal clinical oncology. 5th ed. St Louis: Elsevier Saunders, 2013;321334.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 4.

    Herring ES, Smith MM, Robertson JL. Lymph node staging of oral and maxillofacial neoplasms in 31 dogs and cats. J Vet Dent 2002;19:122126.

  • 5.

    Grosenbaugh DA, Leard AT, Bergman PJ, et al. Safety and efficacy of a xenogeneic DNA vaccine encoding for human tyrosinase as adjunctive treatment for oral malignant melanoma in dogs following surgical excision of the primary tumor. Am J Vet Res 2011;72:16311638.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 6.

    Regan D, Guth A, Coy J, et al. Cancer immunotherapy in veterinary medicine: current options and new developments. Vet J 2016;207:2028.

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