FeLV and lymphoma location in cats: a review of Brazilian studies
Veterinary and animal science · 2025
In plain language
This review brought together studies from Brazil of cats that already had lymphoma. Among these cases, FeLV-positive cats more often had lymphoma in the mediastinum, an area of the chest, and less often had gastrointestinal lymphoma than cats negative for both FeLV and FIV. Because the review included no cats without lymphoma, it cannot determine the risk of developing this cancer in the general cat population. The data vary across studies, and the published figures contain inconsistencies.
Scientific detail
This 2025 systematic review of feline lymphoma associated with FeLV and FIV in Brazil initially identified 29 studies encompassing 607 lymphoma cases. Results Table 1 presents 258 cases: 166 FeLV-positive and 92 FeLV-negative/FIV-negative. The results separately describe 15 FIV-positive/FeLV-negative cases. The abstract reports 273 included cases but lists subgroups of 190, 98, and 15 cases, totaling 303. The supplied text also contains inconsistent association estimates.
Among the reviewed lymphoma cases, FeLV-positive status was significantly associated with mediastinal presentation. Gastrointestinal lymphoma was less frequent among FeLV-positive cases than among FeLV-negative/FIV-negative cases. These observations describe differences in anatomical location among cats that already had lymphoma; they do not establish that FeLV protects against gastrointestinal lymphoma or independently determine these tumors' immunophenotype or grade. The claims have evidence level C.
The review lacked a comparison group of cats without lymphoma and relied on convenience sampling across heterogeneous recruitment settings. The authors identified geographical reporting bias, with research centers in southern and southeastern Brazil overrepresented. Additional limitations included incomplete clinical characterization and staging, few FIV-positive cases, and differences in diagnostic sampling that could affect the representation of intestinal lymphoma subtypes.
The case-only observational design cannot establish the risk of developing lymphoma in the general cat population or a molecular mechanism of FeLV oncogenesis. The geographical distribution of published cases also cannot be treated as a representative map of lymphoma incidence or FeLV-associated oncogenesis across Brazil.
What we know
Among the reviewed lymphoma cases, FeLV-positive status was significantly associated with mediastinal location. Gastrointestinal lymphoma was less frequent among FeLV-positive cases than among FeLV-negative/FIV-negative cases. The evidence is level C and is limited by the absence of cats without lymphoma as a comparison group, selection and geographical biases, incomplete clinical information, and inconsistencies in the text.
What we don't know
This review does not establish the risk of developing lymphoma in the general cat population or a molecular mechanism of FeLV oncogenesis. It also does not establish a protective effect of FeLV against gastrointestinal lymphoma or determine tumor immunophenotype or grade from anatomical location. The inconsistencies prevent reporting a single coherent case count or consistent association estimates; the published geographical distribution does not represent incidence throughout Brazil.
Evidence
EvidenceLevel C — Preliminary evidenceConfidence 100/100
The authors identify geographical reporting bias, with southern and southeastern Brazilian research centers overrepresented.
Excerpt verified in the source — verbatim, in the source's own language“Middle- to high-income areas, where feline medicine and veterinary pathology research groups are concentrated, are overrepresented in the South and Southeast regions. This creates an inherent bias, as these regions have more available data compared to lower-income areas”
The geographical distribution of published cases cannot be treated as a representative map of lymphoma incidence or FeLV-associated oncogenesis throughout Brazil.
EvidenceLevel C — Preliminary evidenceConfidence 100/100
The review lacked a comparison group of cats without lymphoma.
Excerpt verified in the source — verbatim, in the source's own language“The absence of a control group comprising FeLV-positive and FeLV-negative/FIV-negative cats without lymphoma is a limitation of this review, which focused solely on confirmed lymphoma cases”
This author-identified limitation restricts conclusions about the risk of developing lymphoma in the broader cat population. Evidence levels are capped at C because the review lacks this control group.
EvidenceLevel C — Preliminary evidenceConfidence 99/100
Among reviewed lymphoma cases, FeLV-positive status was significantly associated with mediastinal lymphoma.
Excerpt verified in the source — verbatim, in the source's own language“Mediastinal 77 46.4 8 8.7 85 32.9 < 0.0001 * 9.084 (4.170 to 19.070) *”
Table 1 compares 166 FeLV-positive lymphoma cases with 92 FeLV-negative/FIV-negative lymphoma cases. This is an association with anatomical presentation among cats already diagnosed with lymphoma; it does not establish population-level lymphoma incidence or causal oncogenesis. The abstract reports a different estimate.
EvidenceLevel C — Preliminary evidenceConfidence 99/100
Gastrointestinal lymphoma was less frequent among FeLV-positive lymphoma cases than among FeLV-negative/FIV-negative lymphoma cases.
Excerpt verified in the source — verbatim, in the source's own language“Gastrointestinal 15 9.0 51 55.4 66 25.6 < 0.0001 * 0.079 (0.042 to 0.159) *”
The table reports a difference in anatomical presentation within the reviewed lymphoma cases. It does not establish that FeLV protects against gastrointestinal lymphoma, and it does not independently establish the immunophenotype or grade of these tumors.
Provenance
Source: Feline lymphoma associated with feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) infections in Brazil- Systematic review.
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