Volume 58 | Issue 2 Article 12 1996 Canine Oral Malignant Melanoma Adam C. Eiler Iowa State University Kimberly R. Cox Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/iowastate_veterinarian Part of the Neoplasms Commons, and the Small or Companion Animal Medicine Commons Recommended Citation Eiler, Adam C. and Cox, Kimberly R. (1996) "Canine Oral Malignant Melanoma," Iowa State University Veterinarian: Vol. 58 : Iss. 2 , Article 12. Available at: https://lib.dr.iastate.edu/iowastate_veterinarian/vol58/iss2/12 This Article is brought to you for free and open access by the Journals at Iowa State University Digital Repository. It has been accepted for inclusion in Iowa State University Veterinarian by an authorized editor of Iowa State University Digital Repository. For more information, please contact [email protected]. Canine Oral Malignant Melanoma Adam C. Eiler, DVM * Kimberly R. Cox, DVM ** Neoplasia is an all too common find­ Veterinary Diagnostic Laboratory for histo­ ing in domestic animals. The oropharyngeal logic examination, confirming a diagnosis of cavity is a common site for the development oral malignant melanoma. Surgical clear­ of tumors , particularly in dogs. One such tu­ ance at the margins was incomplete. The mor is oral malignant melanoma which owner was notified of the findings and given occurs with some frequency in dogs but is a guarded prognosis for long-term survival rare in cats.! Hence, the following shall fo­ due to the possibility oflocal recurrence and cus on canine malignant melanoma. distant metastasis. "Capricorn" died three years following the Case Study initial diagnosis of oral malignant mela­ noma. Necropsy detected neoplasia of the "Capricorn," a nine year old spayed female liver with no apparent local recurrence of the cocker spaniel, was first presented in Novem­ oral malignant melanoma. The owner ber 1989 for a dental prophylaxis. The owner declined further evaluation of the neoplas­ reported no health problems at the time of tic liver. presentation. During induction of anesthe­ sia, a mass was detected in the oral cavity. Incidence and Prevalence The mass was darkly pigmented and ap­ proximately 1 cm in diameter. It was The oropharyngeal cavity is a prominent site attached via a thin 1 mm diameter pedicle for tumor development. The oral cavity is the to the lower right gingiva lateral to the third fourth most common site of neoplasia in the premolar and 5 mm ventral to the gum line. dog. 2 Approximately 6.6% of all canine The mass was causing no obvious discom­ benign and malignant neoplasms occur in fort; however, the owner elected to have it the oral cavity, most often originating from surgically removed after completing the den­ the buccal mucosa, tongue, periodontium, tal prophylactic procedure. mandible, maxilla, and lips.2 The gingiva, Based primarily on gross appearance, the particularly covering the molars, is the most primary differential was oral malignant common site for oral malignant melanoma melanoma. Therefore, prior to removal, development.3 Tumors of the oral cavity, neither a biopsy nor needle aspirate were regardless of tumor site, are frequently ma­ performed. Thoracic radiographs were not lignant and represent approximately 5.3% taken to evaluate the extent of underlying of all canine malignant tumors.1 bone involvement or distant metastasis. Malignant melanoma is the most common Due to the small attachment area and canine malignant oral neoplasm. A retrospec­ location within the mouth the mass was tive study reported the incidence in a defined removed with approximately 2 mm margins, canine population to be 20.4 cases per every leaving the mandible intact. The mass was 100,000 dogs per year.4 It is 2.5 times more then submitted to the Iowa State University frequent in dogs than cats.1 Breeds report­ edly predisposed to tumor development * Dr. Eiler is a 1996 graduate of the Iowa State include cocker spaniels, golden retrievers, University College of Veterinary Medicine. Labrador retrievers and breeds with darkly ** Dr. Cox is an instructor of small animal surgery 2 at the Iowa State University College of Veterinary pigmented mucosa. ,5 In one study, dachs­ Medicine. hunds and beagles were at a significantly Winter, 1996 79 lower risk at developing oral malignant include measurement of the tumor size, pal­ melanoma.6 Malignant melanoma occurs pation of regional lymph nodes, and a fine most frequently in older male dogs, aging needle aspirate and cytologic examination of 10.1 to 11.5 years.2,6 Based on the reported any enlarged lymph nodes.2 incidence and signalment, oral malignant Radiographs of the skull and thorax are melanoma is a likely cause of "Capricorn's" important to assess the extent of local tu­ tumor. mor invasion and distant metastasis. Skull radiographs should be evaluated for abnor­ Clinical Signs malities associated with the mass such as bone lysis or new bone production. The most As is the case with many diseases, the clini­ useful views are open mouth dorsoventral cal signs of oral malignant melanoma at the or intraoral views ofthe mandible and max­ time of presentation are variable and non­ illa, and oblique lateral projections of the pathognomonic. Some of the more commonly mandible (to visualize each hemimandible reported signs are persistent or recurrent individually). Standard right and left lateral oral hemorrhage, oral pain or a reluctance and dorsoventral views of the thorax are to chew.2 Additional signs include displace­ useful to evaluate the lung fields for meta­ ment or loss of teeth, halitosis, excessive static tumor development.2 salivation, facial deformity, dysphagia, ex­ When available, computed axial tomogra­ cessive licking, and psychogenic phy or magnetic resonance imaging are polydipsia.2,3 Often the only clinical sign re­ useful in defining the area and extent of neo­ ported by the owner is the presence of a mass plastic involvement.2 However, these are not in the oral cavity causing no apparent as frequently done due to the expense and problems, as was the case with "Capricorn." lack of availability. Although none of the aforementioned clini­ By far, the most reliable means of diagno­ cal signs are themselves diagnostic, each is sis and differentiation of tumor type is strongly suggestive of an abnormality involv­ histologic examination of a biopsy sample or ing the oral cavity and requires further fine needle aspirate.2 The diagnostic, micro­ investigation. scopic feature of oral malignant melanoma is the presence of melanocytes (as melano­ Diagnosis mas appear to develop from melanocytes in the oral epithelium).7 Histologic identifica­ While not the only oral tumor in dogs, ma­ tion also relies upon cell shape and nuclear lignant melanoma is the most common. position.5 Melanomas are usually composed Other differential diagnoses include squa­ of intraepithelial nests of polyhedral epithe­ mous cell carcinoma, fibrosarcoma, and lial-like cells that contain abundant granular epulides.2 It is impossible to rely on gross cytoplasm, large hyperchromatic or vesicu­ appearance alone to obtain a definitive lar round nucleoli, and are arranged in diagnosis as these tumors may all look irregular lobules separated by strands of similar. Oral malignant melanomas range collagen.5 The histologic examination allows from amelanotic to heavily pigmented; how­ for differentiating oral malignant melanoma ever, most veterinarians associate melanoma from other oral tumors. Without histologic with the pigmented form, which aids in examination, only a presumptive diagnosis diagnosis.2 can be made. Several routine procedures are recom­ mended to assist in obtaining a diagnosis. A Treatment complete blood count, serum biochemical analysis, and urinalysis are important to The methods of treating oral malignan"t determine overall patient health.2 In addi­ melanoma are numerous. The traditional tion, initial evaluation of an oral mass should forms of treatment include radical surgical 80 Iowa State University Veterinarian Demonstration of Oral Canine Malignant Melanoma. resection, radiation therapy, cryosurgery, ful. The response to radiation therapy is poor chemotherapy, and hyperthermia.8 The for oral malignant melanoma. Hyperthermia choice of treatment method encompasses the alone is ineffective and is used primarily to desires of the owner, capabilities of the clinic, complement radiation therapy. Chemo­ expense and cosmetic results. therapy is usually ineffective. Cryosurgery Ofthe traditional forms, early radical sur­ is often used only as a palliative measure gical excision remains the foundation of for nonresectable tumors.2 Although ineffec­ therapy for most benign and malignant oral tual alone, the above have prolonged tumors.2 Hemimandibulectomy or hemi­ remission time and survival when used as maxillectomy are often the procedure of adjuvant therapy with radical surgery.5 choice. Resection of the tumor requires a A possible alternative treatment to tradi­ minimum 1 cm margin of healthy tissue to tional forms is the use of local, sustained decrease the likelihood of local recurrence.2 release chemotherapy by use ofintralesional Management, however, of oral malignant cisplatin implants.8 The implant is an inject­ melanoma is complicated by the close asso­ able viscous gel composed of a protein carrier ciation with bone and the lack of mobile soft matrix, a vasoactive modifier (epinephrine) tissues within the mouth. This leads to a and a chemotherapeutic drug (cisplatin). difficulty in achieving