PCRfor antigen receptor rearrangement (PARR) clonality testing in a horse with a solitary retropharyngeal lymphoma

Abstract

Summary A 19‐year‐old Quarter Horse gelding was evaluated for respiratory distress and a rapidly enlarging retropharyngeal mass. Initial evaluation revealed severe respiratory distress, and a large, firm mass, visibly appreciable as 12 × 12 cm, in the left retropharyngeal and perilaryngeal region, with surrounding left and right retropharyngeal swelling. No significant abnormalities were present on complete blood count and serum biochemistry analyses. Endoscopy revealed severe pharyngeal collapse restricting airflow without gross abnormalities of the pharyngeal mucosa other than inflammation and irritation. A multilobular retropharyngeal mass, diffusely heterogeneous in echogenicity, was present adjacent to, but not occluding, the carotid artery as assessed by ultrasonography. Initial needle aspirate suggested lymphoma. Tissue biopsy and histopathology confirmed a round cell tumour. A temporary tracheotomy was performed to provide respiratory relief, and the horse was managed on oral antibiotics and anti‐inflammatory medications while awaiting histopathological results. The decision was made to humanely euthanise the horse after biopsy results indicated lymphoma. Definitive diagnosis of T cell rich, large B cell lymphoma was made by combination of cytology, immunohistochemistry and molecular clonality PCR (PARR) testing. Lymphoma should be considered in horses with focal masses of the retropharyngeal region. Although treatment was not pursued, PARR testing was successful in this case and may be helpful for accurate characterisation of lymphoma in horses to more precisely determine prognosis and the most effective treatment plans, as it has been in human patients and small animals.

Cutaneous epitheliotropic T-cell lymphoma in a donkey – a case report

“…Molecular clonality assays, assessing clonality of T- or B-cells through PARR can effectively complete clinical, morphologic, and immunophenotypic assessments [ 21 , 22 ]. Clonality assays are species-specific and in veterinary medicine, are currently only available for dogs, cats, and horses [ 21 – 23 ]. In the present case, the test was performed using primer sets for equine PARR on formalin-fixed paraffin-embedded tissue.…”

T-cell–rich, large B-cell lymphoma in the brain of a horse

“…Although the use of PARR has been described as an adjunct diagnostic test for lymphoma in horses and a donkey, the methods have not been described in detail in the literature. 1,5,8…”

“…4,6,15 The PARR assay is routinely used as an adjunct diagnostic technique in canine and feline lymphoma, and 3 reports describe its application in equine lymphoma and leukemia, although the methods were not provided. 1,5,8 Here we describe the use of the PARR assay for diagnostic confirmation of an equine lymphoma with detailed methods and utilized primers. Because the assay is newly developed, diagnostic sensitivity and specificity have not yet been determined.…”

“…Although the use of PARR has been described as an adjunct diagnostic test for lymphoma in horses and a donkey, the methods have not been described in detail in the literature. 1,5,8 An 8-y-old male Quarter Horse developed anorexia of acute onset. A few hours later, the horse ran uncontrollably into a fence and was placed in a stall overnight for observation.…”

PCR for antigen receptor rearrangement (PARR) in equine veterinary medicine

“…Its reported use in equine veterinary medicine is limited; the case report in this issue describes its use to help confirm a case of T cell‐rich B cell lymphoma (Collar et al . ), and it has also been used to aid the diagnosis of a diffuse large cell lymphoma (Meichner et al . ) and for characterisation of B cell neoplasms (Badial et al .…”