Canine cutaneous epitheliotropic T-cell lymphoma: a review of 30 cases

This retrospective study reviewed the clinical, histological and immunohistochemical features of 30 European cases of canine cutaneous epitheliotropic T-cell lymphoma (CETL). The clinical presentation was highly variable and was not associated with the disease subtype. Diffuse erythema (86.6%) with scaling (60%) and focal hypopigmentation (50%) were the most common lesions. The skin was uniformly involved but muco-cutaneous junctions or mucosae were affected in 50% of cases. The median age at diagnosis was 10 years (SD 2.79, range 4-15) and the median time between onset and final diagnosis was 5 months (SD 3.79, range 0-12). Five cases occurred in Bichon Frises. There was no evidence of a previous history of chronic dermatitis in any cases. Histologically, the follicular epithelium was affected in 86.7% of cases. One case with mainly follicular disease was considered folliculotropic mycosis fungoides (MF), but no follicular mucinosis was observed. Epidermal Pautrier's microabscesses were uncommon (23.3%). Sweat glands were infiltrated in 70% of cases. Immunohistochemistry confirmed T-cell neoplasia in all cases. B cells infiltrated as individual cells or formed linear bands or ectopic follicles at the base of the neoplasm. Ki67 labelling revealed a range of proliferation indices but did not correlate with severity. A final diagnosis of classical MF was made in 40% of the dogs, MF d'emblé in 36.7%, generalized Pagetoid reticulosis in 20% and localized Pagetoid reticulosis in one case (Woringer-Kolopp Pagetoid reticulosis). The median survival time after diagnosis was 6 months and this did not change appreciably with therapy (lomustine or prednisolone).