13 yo Green Iguana

Signalment: 13-year-old, female, Green iguana (Iguana iguana)

Source/ History: Patient presents for mass removal. Mass has grown slightly in size

Microscopic Description:

Expanding the dermis and subcutis is a well-demarcated, unencapsulated, densely cell mass composed of round cells arranged in sheets. The neoplastic cells have distinct cell margins, mild to moderate amounts of eosinophilic, finely granular cytoplasm, round nuclei with finely stippled to vesicular chromatin, and generally one nucleolus. There is mild anisocytosis and anisokaryosis, and occasional binucleated cells. Scattered throughout the mass are small numbers of granulocytes, and occasional plasma cells and lymphocytes. There is hyperkeratosis on the overlying epidermis and multifocal serocellular crusts.

Figure 1. (1X magnification, H&E stain) Skin mass. A well-demarcated and unencapsulated neoplasm expands the dermis and subcutis.
Figure 2. (40X magnification, H&E stain) Neoplastic cells are round, with distinct cell borders and mild to moderate amounts of finely granular eosinophilic cytoplasm. Within the mass are small numbers of scattered granulocytes.
Figure 3. (60X magnification, Giemsa stain) Neoplastic round cells contain positive cytoplasmic metachromatic granules. 

Microscopic Interpretation:

Cutaneous mast cell tumor

Mitotic count: 3 in ten high power fields (total area of 2.37 mm2)

Vascular/lymphatic invasion: Not observed

Margin assessment: Incompletely excised – mast cells are present at the deep margin of the sample in one region. There is a closest lateral margin of 0.2 mm


Mast cell tumors are common skin neoplasms in domestic canines, felines, and ferrets, though they are rarely reported within reptilian species. Multicentric cutaneous mast cell tumors and apparent mastocytosis on peripheral blood have been described in one case report in a common green iguana (Iguana iguana). Due to the rarity of cutaneous mast cell tumors in reptilian species, the exact biological behavior and prognosis is uncertain. Given the findings in the one case report in a common green iguana, evaluation for and monitoring for the potential development of additional tumors is likely warranted.  

References: Reavill, D et al. Conference: Association of Reptilian and Amphibian Veterinarians, 2000. Mast Cell Tumor in a common green iguana (Iguana iguana); Tamlin VS, Bottema CDK, Peaston AE. Comparative aspects of mast cell neoplasia in animals and the role of KIT in prognosis and treatment. Vet Med Sci. 2020 Feb;6(1):3-18.

Case by Joseph Malatos, DVM, DACVP

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