A Curious Chameleon Case
Anatomic pathologist at NationWide Laboratories
(BSc MVB MRCVS DipACVP)
Alison studied veterinary medicine in University College Dublin (UCD). She also undertook an intercalated degree in veterinary pathology at the Royal Veterinary College. After a year in small animal practice she completed her anatomic pathology residency in UCD and became a diplomate of the American College of Veterinary Pathology. Her interests include oncology and exotic animals.
A skin biopsy from a chameleon was received for examination by Nationwide Laboratories. The clinical history was brief and indicated that the animal was male, but the age and species of chameleon were not stated. We were also told that the animal had a mass around the left eye, and other masses elsewhere.
On histologic examination of the mass, interestingly, it appeared to have two somewhat distinct areas. One area appeared as an exophytic nodular mass which resembled a papilloma (Figure 1A). When viewed at higher power, there were epithelial cells palisading along a basement membrane which underwent keratinisation (Figure 2). These epithelial cells were haphazardly arranged with loss of normal layering (Figure 3). There were very abundant mitotic figures and a few cells undergoing individual keratinisation, and there was moderate variation in cell and nuclear size and shape.
The other area of the mass appeared poorly-demarcated, disorganised and infiltrated the dermis (Figure 1B). This area was composed of islands and trabeculae of epithelial cells which frequently underwent keratinisation to form keratin pearls (Figure 4). On higher power, there was very marked cellular atypia, with severe anisocytosis and anisokaryosis, as well as multinucleated cells and multifocal, disorderly keratinisation. Mitotic figures (which were occasionally bizarre in appearance) were seen, as well as apoptotic cells (Figure 5).
In both areas, there were regions of necrosis and heterophilic inflammation
These findings lead us to a diagnosis of squamous cell carcinoma (SCC), albeit a more atypical-appearing one than we typically see in dogs and cats. Given the papilloma-like appearance of the first area described above, we also considered the possibility of an initial “precursor” papilloma which gave rise to SCC (although this was purely speculative).
We turned to the literature for some further information on this condition in chameleons and found a very helpful case series describing multicentric SCC in seven panther chameleons (Meyer et al., 2019). Interestingly, all animals in this case series were male (similar to our “patient”). This report describes the lesions as being multifocal, painless, variable in size, grey and ulcerated, with loss of scale definition. Lesions were located on the dorsal and lateral body wall, eyelid, tail, and the limbs. This paper describes the neoplasms as displaying moderate cellular atypia when examined histologically (which contrasts with the very marked atypia seen in our sample). However, this paper also mentioned papilloma-like lesions, similar to that found in our case. In this case series, two of the animals underwent post-mortem, and were found to have lung metastases.
This study investigated possible causative factors that may gave rise to SCC. Transmission electron microscopy (TEM) was carried out, as was polymerase chain reaction (PCR) for various viruses (papillomavirus, iridovirus, ranavirus, adenovirus and herpesvirus on all samples, and parapox and orthopoxvirus on one sample) but no evidence of viral involvement was found. The possibility of ultraviolet (UV) irradiation as a causative agent was also discussed, given the lesions were located on areas that were exposed to the light, and given that captive reptiles are commonly supplemented with UV light. In three of the cases in this series, based on a discussion of husbandry practises with the owners, it was thought that the animals had been subjected to a higher level of UV light than they would have been in their natural environment.
Interestingly, all the animals in this case series were male, suggesting a sex predilection for SCC in this species. However, the authors believe that this reflects the fact that male chameleons are more often kept as pets than females due to their bright colouration (rather than true sex predisposition).
In this case series, surgical excision was found to be successful in treating individual lesions, but subsequently, new lesions occurred elsewhere. Imiquimod cream was also trialled in one animal as a therapy, but this causes marked inflammation in the adjacent skin, so was discontinued. Two animals underwent cryotherapy. This was partially successful as (based on histologic examination of the treated sites) some lesions completely regressed, but in others, neoplastic tissue remained at the site.
We also found two short case reports discussing this condition in the literature. One describes a case of periorbital SCC which was secondarily infected (Abou-Madi, 2002). This was initially diagnosed as a periorbital abscess. Another case report described the use of implanted carboplatin beads in a cutaneous SCC in a veiled chameleon, which caused a reduction in size of the lesions (Johnson et al., 2016).
- SCC should be considered as a differential diagnosis for skin masses in chameleons, especially those occurring on the head or dorsal/lateral body, and especially if masses are multicentric in distribution.
- The possibility of underlying SCC should be borne in mind in cases of skin abscessation.
- These lesions have the potential to undergo metastasis (especially to the lungs) and clinical staging with thoracic imaging prior to treatment may be advisable.
- Biopsy is required for definitive diagnosis of SCC.
- Ultraviolet light may play a role in the development of these lesions, and over-supplementation should be avoided.
- Surgical excision, cryotherapy or carboplatin bead implantation are potentially-successful treatment options, but further lesions may arise even if initial lesions are successfully removed, and recurrence is possible if neoplastic tissue is not completely excised or
We hope this brief case overview may be helpful to clinicians with an interest in exotics, or to those who only occasionally see reptiles as visitors to their practices.
Figure 2: In Area A, epithelial cells palisade along the basement membrane and undergo keratinisation. H&E, 20x)
Figure 3: In Area A, epithelial cells were haphazardly arranged with loss of normal layering, abundant mitotic figures and moderate variation in cell and nuclear size and shape. H&E, 40x.
Figure 4: In Area B, there were islands and trabeculae of epithelial cells which frequently underwent keratinisation to form keratin pearls. H&E, 5x.
Figure 5: In Area B, there were marked cellular atypia, multinucleated cells, multifocal areas of disordered keratinisation, apoptotic cells and mitotic figures (sometimeses bizarre in appearance) (Figure 5). H&E, 40x.
Abou‐Madi, N. and Kern, T.J., 2002. Squamous cell carcinoma associated with a periorbital mass in a veiled chameleon (Chamaeleo calyptratus). Veterinary ophthalmology, 5(3), pp.217-220.
Johnson, J.G., Naples, L.M., Chu, C., Kinsel, M.J., Flower, J.E. and Van Bonn, W.G., 2016. Cutaneous squamous cell carcinoma in a panther chameleon (Furcifer pardalis) and treatment with carboplatin implantable beads. Journal of Zoo and Wildlife Medicine, 47(3), pp.931-934.
Meyer, J., Kolodziejek, J., Häbich, A.C., Dinhopl, N. and Richter, B., 2019. Multicentric Squamous Cell Tumors in Panther Chameleons (Furcifer pardalis). Journal of exotic pet medicine, 29, pp.166-172.