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)

16 Apr 2020

Baja, A. J., Lewbart, G. A., Luff, J. A., Nolan, M. W.

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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 a 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.