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, there appeared to be two somewhat distinct areas (Figure 1).
One area appeared as an exophytic nodular mass which resembled a papilloma (Area A, Figure 1. 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. There was moderate variation in cell and nuclear size and shape.
The other area of the mass appeared poorly demarcated and disorganised, and infiltrated the dermis (Area B, Figure 1. 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).
Squamous cell carcinoma in chameleons
We turned to the literature for some further information on this condition in chameleons and found a very helpful case series describing multicentric squamous cell carcinoma 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 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-mortems, and were found to have lung metastases.
This study investigated possible causative factors that may give 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 practices 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.
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
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 coloration (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.
Surgical excision was found to be successful in treating individual lesions, but subsequently, new lesions occurred elsewhere
Other mentions of squamous cell carcinoma in the literature
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 and Kern, 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).
- Squamous cell carcinoma 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
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
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.
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