HER2 in Epithelial Tumours of Dogs and Cats
Research activities
Mammary tumours
In feline mammary carcinomas (107 cases, Muscatello et al., Vet Pathol 2019), HER2 gene amplification was characterised for the first time by FISH on dual-core tissue microarrays (TMA), with the development and validation of a BAC probe specific for the feline chromosome E1. Protein overexpression (IHC 3+) was detected in 6.5% of cases and gene amplification in 4%, with a statistically significant correlation between the two.
In canine mammary carcinomas (112 cases, Muscatello et al., Vet Sci 2022), an integrated IHC/FISH analysis was performed using a dual HER2/CRYBA1 probe on chromosome CFA9, preceded by antibody validation via Western Blot on canine cell lines. Protein overexpression (3+) was found in 13.5% of cases and gene amplification in 10%. A novel HER2-CRYBA1 fusion/translocation pattern was identified in 22% of carcinomas — the first such finding in the canine species — together with cases of co-amplification and polysomy. HER2 overexpression was significantly correlated with overall survival (p=0.03).
Pulmonary carcinomas
In feline pulmonary carcinomas (13 cases, Muscatello et al., Vet Pathol 2021), HER2 protein overexpression and gene amplification were evaluated by IHC (two validated antibodies) and FISH. Overexpression (3+) was detected in 15% of cases and amplification in 27%, with a significant association between the two (p=0.03). One amplified case was negative by IHC with both antibodies, suggesting unfavourable pre-analytical conditions or splice variants.
In canine pulmonary carcinomas (19 cases, Brunetti et al., Animals 2024), a combined IHC/FISH/NGS approach was applied for the first time to the same case series. FISH identified gene amplification (cluster type) in 12.5% of evaluable cases. A custom NGS panel covering the full HER2 coding sequence (Molecular Pathology Laboratory, IRCCS Sant'Orsola-Malpighi) detected a V659E transmembrane domain mutation (VAF 29%) in one case — already known as an activating mutation in human and canine lung cancer and likely sensitive to tyrosine kinase inhibitors. This case showed convergence of all three alterations (IHC 3+, FISH amplified, NGS mutated).
Feline nasal carcinomas
In 23 feline nasal carcinomas (Anjomanibenisi et al., Vet Sci 2026), the first systematic immunohistochemical characterisation was performed, evaluating HER2, p53, Ki-67 and PCNA, with digital image analysis (QuPath) for proliferation markers. HER2 was scored 3+ in 30.4% of cases, with a significant association between positivity and adenocarcinoma histotype (p=0.02). These findings identify HER2 as a potential therapeutic target in this tumour type.
Future directions
Canine urinary bladder carcinomas: IHC and FISH on histological sections
The next objective is to apply the established IHC/FISH workflow to the study of HER2 in canine urothelial carcinomas — a tumour type in which HER2 overexpression has been reported but for which systematic data on gene amplification by FISH are lacking. Using the validated canine probes (HER2/CRYBA1 on CFA9), the study will determine the prevalence and cytogenetic patterns of HER2 gene alteration, with potential implications for the use of targeted therapies in this malignancy.
FISH on cytological samples from canine bladder carcinomas
An innovative and clinically relevant goal is the validation and application of FISH on cytological samples from canine urothelial carcinomas. Cytology is often the only diagnostic material available in these patients, as histological biopsy can be technically challenging. Developing a reliable FISH protocol on cytological material would allow non-invasive assessment of HER2 amplification, integrating molecular information with routine cytological diagnosis and opening the way for rapid patient selection for anti-HER2 targeted therapies in veterinary medicine.
