Introduction Zanubrutinib is a second generation Bruton’s tyrosine kinase inhibitor (BTKi) often used to treat B cell malignancies such as marginal zone lymphoma. BTKis belong to a protein tyrosine kinase family that plays an essential role in the proliferation, differentiation, and survival of B cells. The side effects of BTKis include infection, diarrhea, skin rash, and atrial fibrillation. Invasive fungal infections have been previously described with Ibrutinib (a first generation BTKi) but seldom with second generation BTKis such as zanubrutinib.