# Differential HER2 Expression Across Feline Nasal Carcinoma and Its Relationship with Proliferation and p53 Status

## TL;DR

This study examines feline nasal carcinomas, finding that HER2 overexpression is common in adenocarcinomas, suggesting a potential target for future treatments.

## Contribution

The study identifies HER2 as a potential biomarker for feline nasal adenocarcinomas, offering new insights for targeted therapies.

## Key findings

- HER2 overexpression was detected in approximately one-third of feline nasal carcinomas, particularly in adenocarcinomas.
- p53 expression was uncommon and observed exclusively in non-adenocarcinoma tumors.
- Ki-67 proliferation indices were low, while PCNA showed high positivity across all cases.

## Abstract

Feline nasal carcinomas are rare, locally aggressive malignant tumors that typically occur in older cats. Information on their biological and immunohistochemical features is still limited. In this study, 23 feline nasal carcinomas were evaluated to describe their histological characteristics and the expression of selected immunohistochemical markers, including Ki-67, PCNA, p53, and HER2. Most tumors were adenocarcinomas, particularly of the acinar subtype. Ki-67 expression was generally low, while PCNA showed high positivity in all cases. p53 expression was uncommon. Notably, HER2 overexpression was detected in approximately one-third of the tumors, particularly in adenocarcinomas. These results provide baseline immunohistochemical data for feline nasal carcinomas and identify HER2 as a potential biomarker for future diagnostic and therapeutic investigations.

Feline nasal carcinomas are rare but clinically aggressive neoplasms. This study characterizes their histopathological features and evaluates HER2, p53, Ki-67, and PCNA expression using immunohistochemistry and digital image analysis, aiming to provide a comprehensive biological characterization with potential prognostic and therapeutic implications. Tumors were classified into adenocarcinomas (AC) and non-adenocarcinomas (non-AC). Among the 23 cases examined, adenocarcinoma was the most common subtype (17 cases). HER2 was scored as 3+ in 7 cases, 2+ in 8 cases, 1+ in 5 cases, and 3 cases were scored 0. A statistically significant association was found between histological type and HER2 expression (Fisher’s exact test, p = 0.02), with a higher prevalence of HER2 positivity in adenocarcinomas. Evaluation of p53 expression according to histological grouping showed a trend toward significance (p = 0.0593), with p53 positivity observed exclusively in non-AC. The Ki-67 index had a median of 4.4 (min 0.5, max 21.06), and the PCNA index had a median of 82.26 (min 19.55, max 100). No significant associations were identified between the Ki-67 labeling index and HER2 expression, histotype, and the inflammatory infiltrate. Finally, Pearson correlation analysis revealed no significant correlation between Ki-67 and PCNA indices (p = 0.32). The overexpression of HER2 lays the groundwork for the possible use of anti-HER2 targeted drugs in this tumor type, particularly in adenocarcinomas. These findings provide baseline immunohistochemical data for feline nasal carcinomas and highlight HER2 as a relevant biomarker for future diagnostic and therapeutic research.