Fig. 1

Late feline diffuse iris melanoma (FDIM) is a more locally invasive tumour associated with metastatic disease and reduced survival times. Haematoxylin and eosin staining showing the histological progression from iris melanosis (A), to early FDIM (B) and then late FDIM (C). Iris melanosis (A) is characterised by dysplastic melanocytes lining the anterior iris stroma in up to three layers (blue bracket). Progression to early FDIM (B) occurs with invasion of the underlying stroma (blue arrows). In late FDIM (C), neoplastic melanocytes infiltrate the iris, ciliary body and sclera. The blue arrows highlight invasion of the scleral venous plexus. The overview of the clinicopathologic data from the study (D) shows that cats with late FDIM were significantly (p < 0.05) older, had higher mitotic activity, and were the only cats with metastatic disease. Statistically significant differences are indicated by * Kaplan–Meier survival analysis (E) revealed a significantly (p = 0.04) reduced survival time for cats with late FDIM.