Involucrin Expression and Association with Ki-67 in Paraffin Embedded Tissue of Canine Skin Tumors: A Retrospective Study

Abstract

Involucrin (INV) is a cornified envelope precursor protein that is commonly used as an early stage marker of
human terminal keratinocyte differentiation. This research investigated the expression of INV in canine skin tumors
using 56 formalin-fixed paraffin-embedding (FFPE) biopsied specimens. The expression of INV was investigated by
immunohistochemistry (IHC) and RT-PCR. Correlation between INV and Ki-67 was also performed. The malignant
tumor groups showed significantly different INV staining scores and Ki-67 positive cells than the normal skin group
by IHC (p<0.05). The INV scores of moderately differentiated SCC (MSCC), trichoblastoma (TCB), basal cell carcinoma
(BCC) and poorly differentiated SCC (PSCC) significantly decreased, with a statistically significant difference (p<0.05).
Interestingly, the INV of poorly differentiated SCC disappeared in some specimens. The INV expression in most tumors
was found to be inversely proportionate to Ki-67 positive cells. In addition, only SCC regardless of tumor grade without
tumor-graded specimens showed an inversely statistically significant difference between the Ki-67 positive cells and
INV expression (p<0.0001). In RT-PCR, mRNA expression of the FFPE specimens showed substantial similarity of INV
expression as in IHC. It is suggested that the INV expression should be further studied in terms of clinical prognosis in
canine cutaneous SCC.