Idelalisib-associated Enterocolitis: Clinicopathologic Features and Distinction From Other Enterocolitides

Area of Science:

• Oncology
• Gastroenterology
• Pathology

Background:

• Idelalisib, a phosphoinositide-3-kinase δ inhibitor, is approved for chronic lymphocytic leukemia/small lymphocytic lymphoma and follicular lymphoma.
• Idelalisib is associated with severe diarrhea and colitis as known side effects.

Purpose of the Study:

• To describe the histologic findings of idelalisib-associated enterocolitis.
• To aid in differentiating idelalisib-associated enterocolitis from other gastrointestinal conditions.

Main Methods:

• Retrospective review of colon biopsies from 11 patients treated with idelalisib for leukemia.
• Histologic examination including apoptosis assessment, cryptitis, architectural distortion, and inflammatory cell analysis.
• Immunohistochemical stains for cytomegalovirus were performed in a subset of cases.

Main Results:

• All biopsies showed apoptosis within crypts; 5 had moderate to severe apoptosis with goblet cell loss.
• Focal acute cryptitis was present in all cases, with 8 showing mild architectural distortion.
• Increased lamina propria inflammation and intraepithelial lymphocytes (predominantly CD8 T cells) were observed in most cases.

Conclusions:

• Histologic features of idelalisib-associated enterocolitis include apoptosis, cryptitis, and increased intraepithelial lymphocytes.
• Recognizing these features is crucial for distinguishing idelalisib-associated enterocolitis from mimics like graft-versus-host disease and infectious enterocolitis.