Case History

Melanomas are malignant neoplasm orig- inating from melanocytes (Nishiya et al., 2016). They have been described in mam- malians, reptiles and  fishes  (Kimberly  et al 2015; Rahmati-Holasoo et al., 2015; Nishiya et al., 2016). These tumors were less commonly reported in birds. How- ever, they have been identified in a vari-  ety of avian species, including African  grey parrot (Psittacus erithacus erithacus) (Shrader et al., 2016), thick-billed parrot (Rhynchopsitta pachyrhyncha) (Guthrie et al., 2010), zebra finch (Taeniopygia gut- tata) (Irizarry-Rovira et al., 2007), seagull (Larus fuscus) (Costagliola et al., 2001), mandarin duck  (Aix  galericulata)  (Reid  et al., 1993), merlin (Falco columbarius) (Barlow and Girling, 2004), rock hopper penguin (Eudyptes chrysocome)  (Duncan et al., 2014), macaroni penguin (Eudyptes chrysolophus) (Duncan et al., 2014), and Humboldt penguin (Spheniscus humboldti) (Duncan et al., 2014). In this report, we de- scribe cutaneous malignant melanoma in a mallard duck (Anas  platyrhynchos).

Clinical Presentation

In August 2018, a 2-year-old female mal- lard duck (Anas platyrhynchos), at the Qaz- vin nature village was observed with a large palpable and firm mass on the ventral por- tion of the neck (Fig. 1a). Within the previ- ous 1-month period the mass had become distinct and grew larger. No other physical abnormalities were seen. On presentation, the bird was quiet and alert. Appetite and stool appearance were normal. The duck was fed a diet of seeds and plants. Final-  ly, surgical removal of the neoplasm was elected.  The  bird  was  anesthetized   with

Diazepam/Ketamine. A skin incision was made on the ventral surface of the mass and blunt dissection was performed to separate the mass. The incision was sutured by a simple interrupted suture pattern. The mass was removed for histopathological evalu- ation and the bird recovered uneventfully. Enrofloxacin (10 mg/kg IM, once daily for 5 days) was administered IM.

Diagnostic Testing

On gross examination, the mass was firm, black and 10 × 7/5 × 3 cm in size. Tissue samples of the mass were fixed in 10% neutral buffered formalin and routinely processed, dehydrated and embedded in paraffin wax, sectioned at 5 μm thickness (Rotary Microtome RM2 145; Leica) and stained with hematoxylin-eosin (H&E). Additional sections were probed immuno- histochemically for S-100 and Melan-A as described previously (Ramos-Vara et al., 2000). Histopathologically, the mass was mainly composed of infiltrative, pigment- ed melanocytes that extended from superfi- cial to deep dermal regions and had effaced normal tissue architecture (Fig. 1b-c).  In the superficial dermis, the neoplastic me- lanocytes were arranged in various sizes of nests and lobules (Fig. 1b). The neoplastic cells coalesced in the deep dermis, forming dense sheets separated by collagenous stro- ma (Fig. 1c).

Microscopic examination of the sections revealed anaplastic, epithelioid, round to oval to polygonal cells, ranging in size from 18 µm to 90 µm in diameter (giant cells), with eosinophilic cytoplasm containing variable amounts of brown to black    gran-