Study highlights IHC markers for feline nasal lymphoma diagnosis
Bottom line
A new Veterinary Pathology study suggests immunohistochemistry may help clinicians and pathologists better distinguish feline nasal lymphoma from chronic lymphoplasmacytic rhinitis, a common diagnostic challenge in cats with chronic nasal disease. In the study, published online October 12, 2026, investigators evaluated 65 rhinitis cases and 15 diffuse large-cell, immunoblastic nasal lymphomas using markers tied to cell origin, proliferation, DNA repair, apoptosis, and immune regulation. Most lymphoma cases were predominantly CD20/PAX5-positive, consistent with a B-cell phenotype, and showed moderate to strong expression of STAT5, MLH1, MSH2, MSH6, PCNA, and FOXP3. The authors said MLH1, MSH6, and PCNA may be enough as a practical panel in many suspected lymphoma cases. (lifescience.net)
Why it matters: For veterinary professionals, the study speaks to a familiar problem: chronic rhinitis and nasal lymphoma can overlap clinically and even cytologically, delaying a clear diagnosis. Earlier work has shown feline nasal lymphoma is the most common nasal cavity tumor in cats, is often B-cell in origin, and can be misread as inflammatory disease on cytology. A more targeted IHC panel could improve confidence when biopsy findings are equivocal, support earlier treatment planning, and potentially reduce repeat diagnostics for pet parents. (pubmed.ncbi.nlm.nih.gov)
What to watch: The next question is whether these markers hold up in larger, multi-center cohorts and whether they become part of routine diagnostic workflows for feline chronic nasal disease. (lifescience.net)
Key facts
- Study type
- Veterinary Pathology immunohistochemistry study
- Publication date
- Online October 12, 2026
- Cases studied
- 65 lymphoplasmacytic rhinitis cases and 15 diffuse large-cell, immunoblastic nasal lymphomas
- Main diagnostic challenge
- Distinguishing feline nasal lymphoma from chronic lymphoplasmacytic rhinitis
- Key markers
- CD20/PAX5, STAT5, MLH1, MSH2, MSH6, PCNA, FOXP3, and BCL2
- Lymphoma phenotype
- Predominantly CD20/PAX5-positive, consistent with a B-cell phenotype
- Practical panel suggested
- MLH1, MSH6, and PCNA
- Main finding
- Lymphoma cases showed stronger expression of STAT5, MLH1, MSH2, MSH6, PCNA, and FOXP3 than rhinitis cases
A newly published Veterinary Pathology paper adds fresh detail to one of feline medicine’s more frustrating diagnostic gray zones: telling chronic inflammatory rhinitis from nasal lymphoma in cats with persistent upper airway signs. The study, published online October 12, 2026, profiled 80 biopsy-confirmed cases of chronic nasal disease and found that several immunohistochemical markers, especially MLH1, MSH6, and PCNA, may help separate neoplasia from inflammation when routine histopathology alone leaves uncertainty. (lifescience.net)
That matters because feline nasal lymphoma has long been recognized as the most common tumor of the nasal cavity, yet diagnosis isn’t always straightforward. Prior case series found most feline nasal lymphomas are B-cell tumors, but inflammatory cells are often mixed into samples, and some cats with lymphoma are initially read as having lymphoplasmacytic rhinitis on cytology. In one upper respiratory tract lymphoma study, false-negative cytology called lymphoplasmacytic rhinitis occurred in 44% of sampled cases, underscoring how easily inflammation and neoplasia can blur together in real-world practice. (pubmed.ncbi.nlm.nih.gov)
In the new study, authors Sandra Carvalho, Cláudia Marques, Renata M. Gaspar, Rodolfo O. Leal, and Rute M.G. Noiva examined 65 cases of lymphoplasmacytic rhinitis and 15 cases of feline diffuse, large-cell, immunoblastic nasal lymphoma. They used immunohistochemistry to assess lineage markers including CD3, CD20/PAX5, and FOXP3, along with PCNA for proliferation, STAT5 signaling, mismatch-repair proteins MLH1, MSH2, and MSH6, and the apoptosis-related marker BCL2. Most lymphoma cases showed a predominantly CD20/PAX5-positive B-cell phenotype, while inflammatory lymphocytes in both groups were mainly CD3-positive. The lymphoma samples also showed stronger expression of STAT5, MLH1, MSH2, MSH6, PCNA, and FOXP3 than the rhinitis samples. (lifescience.net)
The authors’ practical takeaway is notable: although several markers showed discriminatory value, they suggest a smaller panel of MLH1, MSH6, and PCNA may be sufficient for diagnosing most suspected lymphoma cases. They also propose that the FOXP3-positive, B-cell-predominant profile may point toward a regulatory B-cell phenotype that could contribute to immune evasion. That last point is more hypothesis than practice-ready conclusion, but it adds biologic context that could shape future work on pathogenesis or even therapeutic targeting. (lifescience.net)
There doesn’t appear to be broad outside commentary on the paper yet, but the findings fit with the direction of recent feline lymphoma research. A 2024 congress abstract from the same research track highlighted STAT5, MLH1, MSH2, and PCNA as promising differentiators, and a 2026 gene-expression study in feline nasal lymphoma reported enrichment of tumor-related pathways, including proteasome-associated genes, suggesting that molecular characterization of this disease is expanding beyond basic T-cell versus B-cell phenotyping. (esvp-ecvp-estp-congress.eu)
Why it matters: For veterinarians, especially internists, oncologists, and diagnostic pathologists, this is less about adding another esoteric stain and more about improving decision-making in cats with chronic sneezing, nasal discharge, stertor, epistaxis, or a nondiagnostic workup. Nasal lymphoma can present without an obvious mass, and chronic rhinitis remains a common differential in cats with long-standing nasal signs. If a limited IHC panel can more reliably distinguish proliferation-driven lymphoma from chronic inflammation on biopsy, it could shorten time to treatment, improve prognostic counseling, and help practices explain next steps more clearly to pet parents. (journals.sagepub.com)
The paper also reinforces an older but still important diagnostic lesson: cytology and routine histology may not always be enough on their own. Earlier studies documented that some feline nasal lymphomas are misclassified initially, and that B-cell phenotyping is common in this site, though not universal. In that context, a more standardized IHC approach could be useful when imaging, rhinoscopy, and biopsy findings don’t line up neatly. (pubmed.ncbi.nlm.nih.gov)
What to watch: The next step will be validation, ideally with larger, multi-institution cohorts and clearer performance data on sensitivity, specificity, reproducibility, and cost-effectiveness before a marker panel like MLH1, MSH6, and PCNA becomes a routine recommendation in feline nasal biopsy workups. (lifescience.net)