First-Ever Classification of Dual GI Cancers in Cats Shows Prognosis May Match Single Tumor Cases

Standardized Classification of Synchronous Gastrointestinal Small Cell Lymphoma and Gastrointestinal Mast Cell Tumors in 15 Cats

Ann E. Hohenhaus, Danielle Hudak, Taryn A. Donovan, Christof A. Bertram, Heather Daverio

Background:
Synchronous tumors—two or more independent tumors diagnosed within six months—are recognized in both human and veterinary medicine, but are poorly documented in cats. Gastrointestinal (GI) small cell lymphoma (SCL) is the most common feline alimentary neoplasm, while GI mast cell tumors (MCT) are less frequent but significant. Their simultaneous occurrence is underreported, and no standardized classification exists in veterinary medicine. This study aimed to determine the occurrence, clinical characteristics, and histomorphologic classification (distinct vs. mixed, with mixed subdivided into collision or combined) of synchronous GI SCL and GI MCT in cats.

Methods:
Medical and pathology databases from the Schwarzman Animal Medical Center (USA) and the University of Veterinary Medicine, Vienna (Austria) were reviewed for 2012–2022. Inclusion required histologic confirmation of both GI SCL and GI MCT. Tumors were classified by two blinded board-certified pathologists. Mixed tumors were categorized as collision (adjacent but non-intermingling neoplasms) or combined (adjacent and intermingled populations). Clinical, treatment, and outcome data were extracted for ante-mortem diagnoses.

Results:
Fifteen cats met inclusion criteria, representing 4.3% of 329 AMC cats with GI SCL. Six cats had distinct tumors, six had combined tumors, and three had both distinct and combined tumors. One possible collision tumor was noted. Mean age was 12.2 years; most were domestic shorthair cats. Clinical signs included vomiting, diarrhea, weight loss, and inappetence; four cats were asymptomatic at diagnosis. Ten cats had ante-mortem diagnoses, with survival ranging from 8–1189 days; seven survived beyond 30 days. Treatments included surgery (exploratory celiotomy ± resection anastomosis) and, in some cases, chemotherapy and glucocorticoids. Causes of death included both tumor-related and unrelated conditions.

Limitations:
The retrospective nature limited standardization of biopsy sites and availability of histopathology sections. Some classifications were based on images or reports alone. Variability in tissue sampling may have led to underrecognition of synchronous tumors.

Conclusions:
This is the first veterinary study to classify synchronous tumors in cats as distinct or combined using standardized definitions. Despite concurrent diagnosis of GI SCL and GI MCT, survival outcomes were similar to those reported for cats with either tumor alone. Multiple GI biopsies are recommended for accurate diagnosis, as disease is often multifocal. Adoption of standardized classification terminology will improve reproducibility and cross-study comparisons.

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