Standardized classification of synchronous gastrointestinal small cell lymphoma and gastrointestinal mast cell tumors...

ObjectivesSynchronous primary tumors have been defined as two or more concurrent, yet independent tumors diagnosed within 6 months or less. The primary objective of this study was to investigate the occurrence and clinical findings in cats with synchronous gastrointestinal (GI) small cell lymphoma (SCL) and GI mast cell tumor (MCT) at two referral hospitals. A secondary objective was to classify these tumors as distinct or mixed, and if mixed, categorize them histomorphologically as collision or combined tumors based on standardized definitions informed by literature review.MethodsThe databases of the Schwarzman Animal Medical Center (AMC) and University of Veterinary Medicine in Vienna, Austria (Vetmeduni) were searched between January 2012 and December 2022 for cats with synchronous GI SCL and GI MCT. Clinical findings, treatment and outcome were abstracted from medical records. Biopsy or autopsy reports and, when available, slides and/or histopathology images indicating the presence of a synchronous GI SCL and GI MCT were reviewed by two board-certified pathologists.ResultsA total of 15 cats were diagnosed with synchronous GI SCL and GI MCT, representing 4.3% of 329 cats with GI SCL in the AMC population. This study identified 15 cats with a total of 18 synchronous tumors. Six cats had tumors classified as distinct tumors and six as combined. Three cats had both distinct and combined tumors. Survival in this group of cats was in the range of 8-1189 days.Conclusions and relevanceThis is the first report to classify synchronous tumors in cats as distinct and combined tumors. The results of this study indicate a wide range of survival times for cats with synchronous GI SCL and GI MCT, suggesting that despite the diagnosis of synchronous tumors, the outcome is similar to cats with either GI SCL or GI MCT.