Pathology in Practice

Hao-Kai Chang 1Graduate Institute of Veterinary Pathobiology, National Chung Hsing University, Taichung 402, Taiwan

Search for other papers by Hao-Kai Chang in
Current site
Google Scholar
PubMed
Close
 DVM
,
Pei-Ju Chiang 2Department of Veterinary Medicine, National Chung Hsing University, Taichung 402, Taiwan

Search for other papers by Pei-Ju Chiang in
Current site
Google Scholar
PubMed
Close
 DVM
,
Cheng-Chung Lin 1Graduate Institute of Veterinary Pathobiology, National Chung Hsing University, Taichung 402, Taiwan

Search for other papers by Cheng-Chung Lin in
Current site
Google Scholar
PubMed
Close
 DVM, PhD
,
Hue-Ying Chiou 1Graduate Institute of Veterinary Pathobiology, National Chung Hsing University, Taichung 402, Taiwan

Search for other papers by Hue-Ying Chiou in
Current site
Google Scholar
PubMed
Close
 DVM, PhD
,
Shih-Te Chuang 2Department of Veterinary Medicine, National Chung Hsing University, Taichung 402, Taiwan

Search for other papers by Shih-Te Chuang in
Current site
Google Scholar
PubMed
Close
 DVM, VMD
,
Kuan-Sheng Chen 2Department of Veterinary Medicine, National Chung Hsing University, Taichung 402, Taiwan

Search for other papers by Kuan-Sheng Chen in
Current site
Google Scholar
PubMed
Close
 DVM, MVS, PhD
, and
Yi-Lo Lin 1Graduate Institute of Veterinary Pathobiology, National Chung Hsing University, Taichung 402, Taiwan

Search for other papers by Yi-Lo Lin in
Current site
Google Scholar
PubMed
Close
 DVM, PhD

Click on author name to view affiliation information

History

A 22-year-old 550-kg (1,210-lb) female American Paint Horse used for pleasure riding was evaluated because of progressive inappetence over a period of 1 month and a single episode of hemoptysis that occurred 2 days earlier. No prior pulmonary disease nor cutaneous abnormality had been noticed by the owner.

Clinical and Gross Findings

On physical examination, the horse had a high rectal temperature of 38.9°C (102°F) and low-pitched inspiratory wheezes that were audible during auscultation over the 7th to 12th intercostal spaces of the right side of the thorax and diffusely on the left side of the thorax. Hematologic analysis revealed an inflammatory process (neutrophil count, 9,029 neutrophils/μL [reference interval, 2,500 to 6,900 neutrophils/μL]), hyperfibrinogenemia (fibrinogen count, 600 mg/dL [reference interval, 100 to 400 mg/dL]), and mild anemia (RBC count, 5.42 × 106 RBCs/μL [reference interval, 6.40 × 106 RBCs/μL to 10.4 × 106 RBCs/μL]; hemoglobin concentration, 10 g/dL [reference interval, 10.7 to 16.5 g/L]; and PCV, 27.8% [reference interval, 30.0% to 47.0%]). The clinical and hematologic findings led to a diagnosis of late-stage chronic progressive pneumonia, and the horse was treated with trimethoprim-sulfadiazine (20 mg/kg [9.1 mg/lb], PO, q 12 h), metronidazole (15 mg/kg [6.8 mg/lb], PO, q 8 h), and IV fluid (saline [0.9% NaCl] solution) therapy. However, the horse did not respond well to the medical treatment and the next day, the neutrophil count had increased to 13,310 cells/μL. The horse was recumbent for 6 hours. After it stood up, the horse had difficulty walking and constant tremor and swelling of the left thigh. The horse was weak, but not ataxic. High circulating creatine kinase activity (16,368 U/L; reference interval, 113 to 333 U/L) indicated severe muscle damage. The horse's condition continued to deteriorate, and the animal collapsed again on the fourth day of treatment. High rectal temperature (40.2°C [104.4°F]), hemoptysis, dyspnea, and loud expiratory stridor were noted. On the 10th day after hemoptysis was initially detected by the owner, the horse died.

Postmortem examination revealed a mass on the dorsal aspect of the trachea at the thoracic inlet (Figure 1). Variably sized (1 × 0.5 × 0.5-cm to 8 × 5 × 4-cm), irregular, yellow-white, friable to firm masses, often with central necrosis, were distributed over 30% of the lung parenchyma and diffusely in the pleura on the left side, right 11th rib and intercostal muscle, soft tissue near the T8 vertebra, axillary and mediastinal lymph nodes, round ligament of the uterus, and subcutaneous fat of the abdomen.

Figure 1—
Figure 1—

Photograph of a tumor located at the tracheal bifurcation of a 22-year-old American Paint Horse that was initially evaluated because of progressive inappetence over a period of 1 month and a single episode of hemoptysis that occurred 2 days earlier. The mass is 6 × 7 × 5 cm and white to pale tan, with a friable center.

Citation: Journal of the American Veterinary Medical Association 256, 1; 10.2460/javma.256.1.59

Formulate differential diagnoses from the history, clinical findings, and Figure 1—then turn the page→

Histopathologic Findings

Impression smears of representative masses were stained with modified Romanowsky staina; microscopic examination of the smears revealed many abnormal epithelial cells and a few neutrophils. In sections of the tracheal mass, abundant poorly encapsulated tumor cells were transmural and had invaded and replaced both mucosal and serosal layers of the trachea (Figure 2). Tumor cells were polygonal with distinct intercellular bridges; they were concentrically arranged in trabeculae and nests around central, mature keratin pearls (Figure 3). Cytoplasm of the tumor cells was abundant and eosinophilic, with a large, pale nucleus containing > 2 nucleoli. There were 4 mitotic figures/hpf (400×). The morphology of the metastatic tumor cells in the lungs, axillary and mediastinal lymph nodes, bone marrow cavity of the right 11th rib and intercostal muscle, soft tissue near the T8 vertebra, and the round ligament of the uterus was similar to that of the cells in the tracheal mass.

Figure 2—
Figure 2—

Photomicrograph of a section of the affected portion of the trachea of the horse in Figure 1. The mass was transmural and affected the mucosa through the serosa of the trachea. H&E stain; bar = 1.0 mm.

Citation: Journal of the American Veterinary Medical Association 256, 1; 10.2460/javma.256.1.59

Figure 3—
Figure 3—

Photomicrographs of sections of the tracheal tumor of the horse in Figure I. A—The tumor cells are arranged in nests around keratin pearls (asterisks). H&E stain; bar = 200 urn. Inset—Some tumor cells have distinct intracellular bridges (arrows). H&E stain; bar = 50 μm. B—The tumor cells were positive for p63. p63-specific immunohistochemical stain; bar = 100 μm.

Citation: Journal of the American Veterinary Medical Association 256, 1; 10.2460/javma.256.1.59

Because the pleura on the left side was involved, immunohistochemical analyses for mesothelin (mesothelial cell origin marker), vimentin (mesenchymal cell origin marker), pancytokeratin (epithelial cell origin marker), and p63 (squamous differentiation marker) were applied to sections of the tracheal mass to determine whether the neoplasm was of mesothelial or epithelial cell origin. The tumor cells were positive for p63 and pancytokeratin but negative for vimentin and mesothelin (data not shown), which yielded a classification of malignant squamous cell carcinoma (SCC).

Morphologic Diagnosis and Case Summary

Morphologic diagnosis: SCC of the trachea with widespread metastases to lung, axillary and mediastinal lymph nodes, bone marrow of the right 11th rib and intercostal muscle, soft tissue around the T8 vertebra, round ligament of the uterus, and subcutaneous fat in the abdomen.

Case summary: SCC originating from the trachea with systemic metastasis in a horse.

Comments

Squamous cell carcinoma is a very common skin neoplasm in horses. Respiratory mucosal SCC also develops in horses, and the nasal and paranasal sinuses are common sites.1 However, malignant tracheal tumors in horses are rare. Intratracheal SCCs in an 18-year-old Arab cross and a 35-year-old Morgan horse have been reported.2 In humans, the incidence of tracheal tumors is also quite low and among such tumors SCC is the most common type. These usually develop in the lower portion of the trachea. Neoplasia of the pulmonary parenchyma is also very rare in horses, and granular cell tumor is the most frequently reported type. Bronchogenic SCCs in 3 horses with hypertrophic osteopathy3 and a horse without clinical signs of pulmonary neoplasia have been described.4

For the horse of the present report, it was difficult to definitively assign either the trachea or lung tissue as the primary site of the SCC. However, on balance, a tracheal origin seemed the more reasonable assumption, largely because the degree of tumor cell differentiation in the trachea was greater than that in the lungs. Therefore, it was inferred that tumor cells metastasized from the tracheal mucosa into lung parenchyma through the respiratory tract and subsequently implanted into the pleura.

In the horse of the present report, tumor sites also included abdominal tissues. Gastric SCC represents 3% to 4% of all SCCs in horses and is the most common primary neoplasm of the equine gastrointestinal tract.5,6 Gastric SCC is most common in older horses with a possible connection to recurrent gastric ulceration or lesions in the stomach caused by nematodes of the genus Habronema.7,8 Gastric SCC commonly metastasizes to the thoracic cavity, and liver and intestinal metastases have also been reported.9,10 In the horse of the present report, no neoplastic cells were found in the stomach, liver, or intestines. Therefore, the tumor masses found in the abdominal subcutaneous fat and round ligament of the uterus were likely a result of metastasis from neoplastic tissues of the trachea or lungs. The involvement of both axillary and mediastinal lymph nodes may have been evidence of lymphatic metastasis; however, hematogenous spread may also be possible given that tumor masses were present in multiple tissues.

Carcinoma of the thoracic cavity tissues should be differentiated from mesothelioma and other tumors that originate from lung tissue.11 The horse of the present report did not have clinical signs (pleural effusion and ascites) that are typically associated with mesothelioma. The histopathologic characteristics of the tracheal mass, namely the arrangement of cells in trabeculae and islands around central, mature keratin pearls, made the diagnosis of mesothelioma highly unlikely. Furthermore, tumor cells in affected portions of the lungs and trachea were positive for pancytokeratin and p63 and negative for vimentin, which indicated that the cells originated from ectoderm. Therefore, a diagnosis of SCC was made for the horse of the present report.

The horse was at a very advanced stage of the disease when hemoptysis was observed, yet the owner did not report notable respiratory tract signs. Human tracheal SCC is usually diagnosed late despite its fast growth because of delayed development of specific symptoms, of which hemoptysis, dyspnea, cough hoarseness, and stridor are the most common.12,13 Euthanasia is generally recommended for horses with thoracic neoplasia because of the extremely poor prognosis.14 In the case described in the present report, the horse died a few days after hemoptysis developed while the owner was still considering the option of euthanasia.

Footnotes

a.

Modified Romanowsky stain, Diff-Quik, Sysmex, Kobe, Japan.

References

  • 1. Madewell BR, Priester WA, Gillette EL, et al. Neoplasms of the nasal passages and paranasal sinuses in domesticated animals as reported by 13 veterinary colleges. Am J Vet Res 1976;37:851856.

    • Search Google Scholar
    • Export Citation
  • 2. Sweeney CR. Trachea and bronchi. In: Traub-Dargatz JL, Brown CM, eds. Equine endoscopy. 2nd ed. St Louis: Mosby, 1997.

  • 3. Lavoie JP, Carlson GP, George L. Hypertrophic osteopathy in three horses and a pony. J Am Vet Med Assoc 1992;201:19001904.

  • 4. Schultze AE, Sonea I, Bell TG. Primary malignant pulmonary neoplasia in two horses. J Am Vet Med Assoc 1988;193:477480.

  • 5. Cotchin E. A general survey of tumours in the horse. Equine Vet J 1977;9:1621.

  • 6. Sundberg JP, Burnstein T, Page EH, et al. Neoplasms of equidae. J Am Vet Med Assoc 1977;170:150152.

  • 7. Knottenbelt DC, Snalune K, Kane JP. Squamous cell carcinoma. In: Knottenbelt DC, Snalune K, Kane JP, eds. Clinical equine oncology e-book. Edinburgh: Elsevier Ltd, 2015;220234.

    • Search Google Scholar
    • Export Citation
  • 8. Pascoe RR, Knottenbelt DC. Neoplastic conditions. In: Byers C, Parr C, eds. Manual of equine dermatology. London: WB Saunders, 1999;261266.

    • Search Google Scholar
    • Export Citation
  • 9. Taylor SD, Haldorson GJ, Vaughan B, et al. Gastric neoplasia in horses. J Vet Intern Med 2009;23:10971102.

  • 10. Tennant B, Keirn D, White K, et al. Six cases of squamous cell carcinoma of the stomach of the horse. Equine Vet J 1982;14:238243.

  • 11. Couetil L, Hawkins JF. Abnormal respiratory sounds. In: Couetil L, Hawkins JF, eds. Respiratory diseases of the horse: a problem-oriented approach to diagnosis and management. London: Manson Publishing Ltd, 2013;151200.

    • Search Google Scholar
    • Export Citation
  • 12. Goldstein J. Primary carcinoma of the trachea: report of two cases. South Med J 1977;70:434436.

  • 13. Webb BD, Walsh GL, Roberts DB, et al. Primary tracheal malignant neoplasms: the University of Texas MD Anderson Cancer Center experience. J Am Coll Surg 2006;202:237246.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 14. Satue K, Munoz A, Gardon JC. Interpretation of the equine leukogram. J Hematol Res 2014;1:2735.

All Time Past Year Past 30 Days
Abstract Views 111 0 0
Full Text Views 807 682 41
PDF Downloads 281 138 26
Advertisement