Invasive Cutaneous Mucormycosis in a Patient With Chronic Lymphocytic Leukemia on Obinutuzumab, Idelalisib, and Bruton Tyrosine Kinase Degrader: A Case Report

Invasive fungal infections (IFIs) due to <i>Mucorales</i> are a significant infectious complication in patients with hematologic malignancy, contributing to high mortality rates. The emergence of new targeted biologic therapies has introduced additional effects on the innate and humoral immune system, which produce variable risk for IFIs. Timely diagnosis and treatment of invasive mucormycosis can be challenging. We present a case of invasive cutaneous mucormycosis in an elderly man with chronic lymphocytic leukemia (CLL), who was receiving a Bruton tyrosine kinase (BTK)-targeted protein degrader trial drug (BGB-16673), obinutuzumab, a newer anti-CD20 monoclonal therapy, and idelalisib, a phosphoinositide 3-kinase inhibitor. While molecular testing and tissue culture were negative, histopathology was essential to early diagnosis. Clinical cure was achieved with limb amputation, given the extent of disease. This case underscores the necessity of a low index of suspicion for mucormycosis on presentation, critical appraisal of the patient's risk factors, and a multimodal approach to diagnosis.