Histopathologic, phenotypic, and molecular criteria to discriminate low‐grade intestinal T‐cell lymphoma in cats from lymphoplasmacytic enteritis

Abstract

Background Differentiation of low‐grade intestinal T‐cell lymphoma (LGITL) from lymphoplasmacytic enteritis (LPE) in cats is a diagnostic challenge for pathologists. Objective Characterize histologic, immunohistochemical, and molecular features of LGITL and LPE. Animals Forty‐four client‐owned cats, 22 diagnosed with LGITL and 22 with LPE. Methods Prospective, cohort study. Clinical suspicion of LGITL or LPE was based on persistent gastrointestinal signs, unresponsive to empirical treatments. All cats underwent a standardized diagnostic evaluation, including biopsy (preferentially full‐thickness), and were diagnosed with LGITL or LPE after review of clinical, laboratory, sonographic, histologic, immunohistochemical, and clonality results. Results A monomorphic lymphocytic population (22/22, 100%) and in‐depth mucosal infiltration (15/22, 68%) were hallmarks of LGITL. Epithelial patterns (nests and plaques) were significantly more frequent in LGITL (11/22, 50%) than in LPE (1/22, 5%) cases (P = .001). A CD3+ lymphocytic apical‐to‐basal gradient was observed in 9/22 (41%) of LGITL vs 1/22 (5%) of LPE cases (P = .004). Most LPE cases (17/18, 94%) featured marked fibrosis in the superficial part of the lamina propria. The Ki‐67 20%‐ and 30%‐thresholds discriminated between LGITL and LPE within both the epithelium (specificity >95%) and lamina propria (specificity >95%), respectively. All LGITL cases were CD3+ pSTAT3− and pSTAT5+. T‐cell receptor gamma chain gene rearrangements indicated monoclonality in 86% of LGITL cases. Surprisingly, 70% of LPE cases featured monoclonality (40%) or monoclonality on a polyclonal background (30%). Conclusions and Clinical Importance We identified new histologic, immunohistochemical, and clonality criteria to distinguish LGITL from LPE.

Clinical, laboratory and ultrasonographic findings differentiating low‐grade intestinal T‐cell lymphoma from lymphoplasmacytic enteritis in cats

“…Our study was prospectively conducted at the same referral center, Alfort School of Veterinary Medicine, Paris, France, between July 2016 and July 2018. 31 All data were prospectively acquired, except for ultrasonographic features, which were retrospectively and blindly reviewed. The study was approved by the ethical committee of our institution (ENVA COMERC n°2016‐05‐09), and all owners gave informed, written consent for all of the investigations.…”

“…The epithelium and lamina propria were reviewed separately, as presented in the companion article. 31 Because human medical and veterinary classification systems tend to use overlapping criteria, samples were classified according to criteria of the World Small Animal Veterinary Association (WSAVA) Gastrointestinal Standardization Group, 34 the revised 2016 World Health Organization (WHO) classification of lymphoma in humans, 34 the WHO classification of lymphoma in dogs and using a veterinary textbook. 35 As presented in the companion article, 31 clonality results were discussed with a human medical specialist in lymphoproliferative disorders (Maria‐Elena Turba, Laboratorio Genefast, Forli, Italy).…”

“… 31 Because human medical and veterinary classification systems tend to use overlapping criteria, samples were classified according to criteria of the World Small Animal Veterinary Association (WSAVA) Gastrointestinal Standardization Group, 34 the revised 2016 World Health Organization (WHO) classification of lymphoma in humans, 34 the WHO classification of lymphoma in dogs and using a veterinary textbook. 35 As presented in the companion article, 31 clonality results were discussed with a human medical specialist in lymphoproliferative disorders (Maria‐Elena Turba, Laboratorio Genefast, Forli, Italy). Uncertain cases were characterized by criteria applicable to both diseases (eg, coexistence of lymphocytic and neutrophilic cryptitis, monomorphic small lymphocytes within a polymorphic background).…”

“…These cases ultimately were discussed between both pathologists to find an agreement, as discussed in the companion article. 31 …”

“…Recently, new histologic and immunohistochemical features for LGITL have been suggested. 17 , 30 In a companion article, 31 we reported new histopathologic criteria to discriminate LGITL from LPE in a cohort of cats. Using the same cohort, the current study aimed to determine whether discriminatory clinical, laboratory and ultrasonographic results can help differentiate LGITL from LPE.…”