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. 2020 Jun;8(2):e001039.
doi: 10.1136/vetreccr-2019-001039. Epub 2020 Apr 16.

Unexpected but transient tumour enlargement preceded complete regression and long-term control after irradiation of squamous cell carcinoma in a red-eared slider (Trachemys scripta elegans)

Alexia J Baja  1 , Gregory A Lebart  1 , Jennifer A Luff  2 , Michael W Nolan  1
Affiliations

Unexpected but transient tumour enlargement preceded complete regression and long-term control after irradiation of squamous cell carcinoma in a red-eared slider (Trachemys scripta elegans)

Alexia J Baja et al. Vet Rec Case Rep. 2020 Jun.

Abstract

A red-eared slider with a chronic non-healing ulcerative shell lesion was diagnosed with cutaneous squamous cell carcinoma (SCC). The animal underwent surgical debulking, and adjuvant hypofractionated radiation therapy. The lesion initially responded, with near complete tumour regression, but then began growing again just a few months after finishing radiotherapy. Then, after several months with no additional tumour-directed therapy, the lesion again regressed. Five years post-irradiation and with no further treatment, the turtle now remains tumour-free. This unusual pattern of disease regression followed by transient growth and then long-term local tumour control suggests either spontaneous remission, or a pseudoprogression-like phenomenon. Careful clinical follow-up and reporting of future cases will aid in determining whether this pseudoprogression-like event was random, versus being a common component of the chelonian response to irradiation of cutaneous SCC.

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Figures

Figure 1:
Figure 1:
Transverse section of a computed tomography scan that was used for radiotherapy planning. Radiation was delivered to the gross tumour volume (red; GTV), a 1 centimeter clinical target volume that was bounded by the body wall (orange; CTV), and an isotropic 0.5 centimeter planning target volume (magenta; PTV) expansion. Radiation was prescribed such that 95% of the PTV received 32 Gy total.
Figure 2:
Figure 2:
Post-irradiation histopathology of a proliferative mass at the treatment site revealed nests of neoplastic squamous epithelial cells with abundant eosinophilic cytoplasm, marked anisocytosis and anisokaryosis, and frequent keratin pearls consistent with recurrent SCC; the black arrows identify a representative example of one such nest.
Figure 3:
Figure 3:
The previously irradiated cutaneous squamous cell carcinoma in a red-eared slider is depicted in this photograph, taken 5 years post-irradiation; it shows healthy tissue that is grossly devoid of tumour, thus documenting complete and spontaneous tumour regression after initial apparent treatment failure characterized by tumour enlargement.
See this image and copyright information in PMC

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