Idelalisib-associated Colitis: Histologic Findings in 14 Patients

Idelalisib is an inhibitor of the PI3Kδ isoform approved for treatment of patients with relapsed chronic lymphocytic leukemia and indolent non-Hodgkin lymphoma. Many patients develop gastrointestinal symptoms during idelalisib therapy; however, the pathologic effects of this drug have not been characterized. We identified 50 patients who received at least 3 months of idelalisib therapy. Clinical findings and symptoms were noted for each patient, and endoscopic findings were recorded for those who underwent colonoscopic examination. Hematoxylin and eosin–stained sections from colonic biopsy samples were evaluated for histologic patterns of injury. Twenty-three (46%) patients experienced diarrhea during treatment with idelalisib, including 8 with severe symptoms (≥7 stools/d above baseline and/or requiring hospitalization). Fourteen patients underwent colonoscopic examination with mucosal biopsy. Twelve (86%) of these had colitis characterized by intraepithelial lymphocytosis, crypt cell apoptosis, and neutrophilic infiltration of crypt epithelium. Eleven patients had symptoms severe enough to warrant drug withdrawal, including 9 who were also treated with corticosteroids. Idelalisib commonly causes diarrheal symptoms in patients undergoing therapy for B-cell neoplasia, which may be severe in nearly 20% of patients. Characteristic histologic features include the combination of intraepithelial lymphocytosis and crypt cell apoptosis, often accompanied by neutrophils. Discontinuation of the drug results in symptomatic improvement and resolution of histologic changes.