Feline lymphoma in Croatian pathology records: anatomical patterns and association with FeLV
Veterinary sciences · 2025
In plain language
The study described 188 lymphoma cases in cats referred for assessment in Croatia. The authors observed an association between FeLV and lymphoma in the mediastinum, an area of the chest, but this does not show that FeLV caused those tumors. Only approximately 21% of cases were tested for FeLV/FIV, with testing favoring younger cats with lymphoma in that area. These results cannot tell us how common that association is among all cats with lymphoma or in the general cat population.
Scientific detail
This retrospective clinical study, published in Veterinary Sciences in 2025 (doi: 10.3390/vetsci12100986), described 188 lymphoma cases among 5478 feline referrals. Immunohistochemistry was performed on 153 samples, and anatomical classification was available for 128 cases. Among the anatomically classified cases, multicentric, alimentary and mediastinal forms accounted for 27.3%, 26.6% and 25%, respectively. These proportions describe anatomically classified pathology referrals, not lymphoma incidence in Croatia's general cat population.
The reported immunophenotype distribution varied by anatomical site: mediastinal lymphoma was almost exclusively T-cell, whereas alimentary lymphoma was predominantly B-cell. Elsewhere, the source describes mediastinal cases as exclusively T-cell, creating uncertainty about the exact distribution. This anatomical association does not demonstrate that FeLV specifically caused the T-cell tumors.
The discussion reports that approximately 21% of cases underwent FeLV/FIV testing and records 32 positive cats, without reporting the exact number tested or separate counts for each virus. Testing preferentially involved younger cats with mediastinal lymphoma. The authors describe an association between FeLV infection and mediastinal lymphoma, with nearly 70% of FeLV-positive cats classified as having mediastinal disease. However, the passage combines FeLV/FIV positivity reporting with a FeLV-specific association and provides neither an association effect estimate nor its uncertainty.
All four claims have evidence level C. Interpretation is limited by referral and pathology-submission bias, possible anatomical misclassification based on submitted samples, and selection of cats for viral testing. Small breed-specific referral denominators and wide confidence intervals also limit breed-specific findings. The data do not establish FeLV causation or provide an unbiased estimate of viral positivity among all lymphoma cases or in the general cat population.
What we know
In this retrospective series, anatomical site was associated with lymphoma immunophenotype. The authors also reported an association between FeLV and mediastinal lymphoma, with nearly 70% of FeLV-positive cats classified as having mediastinal disease. These observations have evidence level C and are limited by selection of cases and of cats undergoing testing.
What we don't know
The exact number of cats tested for FeLV/FIV and separate positive counts for each virus are not reported. No effect estimate or uncertainty is provided for the FeLV association, and the source is inconsistent about whether mediastinal lymphomas were almost exclusively or exclusively T-cell. The study does not establish that FeLV caused these tumors or determine population lymphoma incidence or a generalizable viral positivity proportion.
Evidence
EvidenceLevel C — Preliminary evidenceConfidence 100/100
The reported immunophenotype distribution varied by anatomical site, with mediastinal lymphoma almost exclusively T-cell and alimentary lymphoma predominantly B-cell.
Excerpt verified in the source — verbatim, in the source's own language“In our data, the distribution of B- versus T-cell lymphoma depended strongly on anatomical type: mediastinal lymphomas were almost exclusively T-cell, whereas alimentary lymphomas were predominantly B-cell ( Table 3 ).”
This is an anatomical association in a retrospective series. It does not demonstrate that FeLV specifically caused the T-cell tumors. Elsewhere the source calls mediastinal cases exclusively T-cell, creating uncertainty about the exact distribution.
EvidenceLevel C — Preliminary evidenceConfidence 100/100
Among 128 lymphoma cases with anatomical classification, multicentric, alimentary and mediastinal forms accounted for 27.3%, 26.6% and 25%, respectively.
Excerpt verified in the source — verbatim, in the source's own language“Anatomical classification was available for 128 (68.1%) of the lymphoma cases. Among these, multicentric lymphoma was the most common subtype (35, 27.3%), followed by alimentary (34, 26.6%), mediastinal (32, 25%), and extranodal lymphomas (27, 21.1%).”
These proportions describe anatomically classified pathology referrals, not lymphoma incidence in the general Croatian cat population.
EvidenceLevel C — Preliminary evidenceConfidence 100/100
FeLV/FIV testing preferentially involved younger cats with mediastinal lymphoma, limiting the generalizability of the reported viral associations.
Excerpt verified in the source — verbatim, in the source's own language“We should note that FeLV/FIV testing in our study was performed mainly in younger cats, most of which had mediastinal lymphoma. This biased testing pattern likely explains the high apparent prevalence and limits the generalizability of FeLV/FIV associations to the broader population.”
The authors explicitly identify selection bias; the reported positivity proportion cannot be treated as an unbiased estimate for all lymphoma cases or the general cat population.
EvidenceLevel C — Preliminary evidenceConfidence 98/100
The authors report an association between FeLV infection and mediastinal lymphoma, with nearly 70% of FeLV-positive cats classified as having mediastinal disease.
Excerpt verified in the source — verbatim, in the source's own language“Among lymphoma cases, 32 cats (75% of those tested for FeLV/FIV) were positive for these viruses, representing 17% of all lymphoma cases in the study, with a strong association between FeLV infection and mediastinal lymphoma, as nearly 70% of FeLV-positive cats fell into this category followed by multicentric lymphoma.”
The passage combines FeLV/FIV positivity reporting with a FeLV-specific association. It does not provide separate viral counts, an association effect estimate or uncertainty, and does not establish causation.
Provenance
Source: Feline Lymphoma in Focus: Examining the Patterns and Types in Croatia's Pathological Records.
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