Novel use of immunohistochemistry for phenotypic evaluation of circulating neoplastic lymphocyte populations

A 5-year-old male neutered Poodle cross presented with a 2-week history of non-specific gastrointestinal signs including vomiting, inappetence and lethargy (Case 1). A 14-year-old male neutered Staffordshire Bull Terrier presented with a 6-week history of progressive inappetence and lethargy (Case 2).

On presentation, Case 1 was dehydrated and had repeatable cranial abdominal pain. Mild hypoproteinemia with hypoalbuminemia, and electrolyte disturbances were found on biochemistry profile. Abdominal ultrasonography showed moderate diffuse small intestinal wall irregularity and moderate local lymphadenopathy. Haematology was repeated 2 days after initial presentation and showed a marked leucocytosis associated with an elevated circulating neoplastic cell population. On presentation, Case 2 was dehydrated, had palpable hepatomegaly and a mild generalised lymphadenopathy. A low number of large, atypical lymphocytes were found on haematology. Sonographically there was hepatomegaly with diffuse parenchymal changes and severe mesenteric lymphadenopathy.

Aspirates from the abdominal lymph nodes (Cases 1 and 2) and liver (Case 2), and blood smears revealed atypical neoplastic lymphoid populations, predominantly comprising large lymphocytes. Immunocytochemistry failed to determine the lymphoid phenotype in Case 1 but supported a T cell phenotype in Case 2. Immunohistochemistry of formalin-fixed paraffin-embedded (FF-PE) blood clots was able to identify a T cell phenotype in both cases. PCR for antigen receptor rearrangement results from both cases were consistent with an expanded T cell population.

In both cases, immunohistochemistry on FF-PE blood clots revealed a circulating T cell lymphocyte population, consistent with T cell lymphoproliferative neoplasia.

Immunohistochemistry on FF-PE blood clots offers clinicians a reliable, inexpensive and minimally invasive method of phenotyping neoplastic cells in circulation. Compared to other available methods, prolonged sample stability allowing for transport and retrospective examination is a distinct advantage. This technique should be considered a useful adjunct to the currently available methods for the phenotypic evaluation of lymphoid leukaemia in dogs.