Evaluation of Ki-67 expression in feline non-ocular melanocytic tumours

Abstract

BackgroundMelanomas are rare in cats. The eye is the most commonly involved site, whereas few data are available about feline non-ocular melanomas (NOMs). Ki-67 thresholds with prognostic relevance have been established for canine melanomas, but not in cats. This study was undertaken to investigate the relationship between Ki-67 index, tumour characteristics, and clinical outcome in feline NOMs.Histologic samples were retrospectively reviewed. Amelanotic tumours were admitted upon immunohistochemical positivity for Melan A or S100. Evaluated parameters included morphological diagnosis, histotype, junctional activity, degree of pigmentation, vascular invasion, lymphocytic infiltrate, necrosis, mitotic count (MC) and Ki-67 index. Pigmented tumours were bleached before evaluation. Clinical and follow-up information were retrieved via telephone interviews with the referring veterinarians.ResultsFifty tumours located in skin (n = 33) and mucosae (n = 17) were included. Forty-eight percent and 95% of amelanotic tumours (n = 21) stained positive for Melan A and S100, respectively. Most achromic tumours were mucosal (P < 0.001, Fisher’s exact test) and presented a spindle cell morphology (P = 0.002; Fisher’s exact test). MC and Ki-67 index were significantly correlated (P < 0.001; R = 0.67; Spearman’s rank correlation); median values were 15 (range, 0–153) and 28% (range, 1–78%), respectively. Both were significantly higher in spindle cell melanomas, in tumours lacking junctional activity and in poorly-pigmented tumours. Follow-up information was available for 33 cats (66%). Variables related with a poor clinical outcome included mucosal location, tumour size, spindle, balloon and signet ring cell histotypes, low pigmentation, MC > 5, Ki-67 > 20% and lack of treatment administration. On multivariable analysis, only tumour histotype and treatment retained prognostic significance.ConclusionsAlthough the majority of feline NOMs behave aggressively, Ki-67 index, together with other parameters, may contribute to prognostic assessment. Prospective studies on homogeneous populations are warranted to identify reliable threshold values for this marker.

Malignant Melanoma on the Nasal Planum Treated with Nasal Planectomy in a Cat

“…Cats were more likely to develop NOMTs in the tissues of the head 3,7,9) , but the incidence of nasal NOMTs was rare (4%) 9) . Histologically, non-pigmented NOMTs, like the one in the case described here, comprised 10-42% 3,[9][10][11] of cases, and the mixed epithelial-spindle cell type accounted for 7-33% 9, 10) of cases. Histologically, 57% (12/23) 9) and 46% (36/79) 7) of cases in previous studies were reportedly malignant and high-grade, respectively, although clear criteria for malignancy…”

“…In previous reports of NOMTs in cats, the median or mean age at onset was 11 years, and there was no sex predilection [7][8][9]11) . Cats were more likely to develop NOMTs in the tissues of the head 3,7,9) , but the incidence of nasal NOMTs was rare (4%) 9) .…”

“…In cats, non-ocular melanocytic tumors (NOMTs) are rare and have been reported to account for approximately 0.5% of all skin tumors 12) . Although histological criteria for malignancy is not yet established for NOMTs, their clinical behaviors often indicate malignancy; recurrence and/or metastasis is reportedly observed in 31-67% 3,7,8) , and tumor-related death is reported in 54-58% 9,11) of cases. NOMTs with histologically apparent malignant features are classified as malignant melanomas and have a poor prognosis 7) ; aggressive surgery is considered the best treatment option.…”

Histological Classification and Immunohistochemical Study of Feline Colorectal Epithelial Tumors

“…Moreover, it is important to note that the degree of differentiation, which was evaluated by gland formation, was moderately associated with malignancy irrespective of the histopathological subtype. On the other hand, the Ki67 labeling index, widely considered to be a prognostic factor in many tumors in humans and cats, 2,22,30,37,38 was not related to the malignancy of feline colorectal tumors. This discrepancy may result from the specific characteristic of intestinal epithelial cells that they have high proliferative activity even in normal tissue.…”

Melanocytic tumours of the nasal planum in cats: 10 cases (2004–2019)

“…According to Sabattini et al . (2018), clean margins correlated with a better outcome. Complete surgical resection of tumours arising on the nasal planum can be challenging or radical resections may be declined by owners which could potentially contribute to a poorer survival.…”