Antifungal Minimal Inhibitory Concentrations of Mold Isolates from Patients with Cancer; Single-Center Experience, 2018–2023

The increasing emergence of antifungal resistance poses potential clinical challenges, particularly among immunocompromised patients with cancer at risk of invasive mold infections, but data on antifungal susceptibility trends specific to this population are few. We evaluated distributions of minimal inhibitory concentrations (MIC), including minimal effective concentrations (MEC) for echinocandins, of 11 antifungal agents for 523 mold isolates (395 <i>Aspergillus</i> spp.) from cancer patients. Based on published Clinical and Laboratory Standards Institute guidelines, isavuconazole had notably high rates of non-wild-type MICs for <i>A. fumigatus</i> (19.6%), <i>A. flavus/oryzae</i> (34.8%), <i>A. niger</i> complex (26.1%), and <i>A. terreus</i> complex (8.33%). Persistent low baseline resistance of <i>A. fumigatus</i> to voriconazole was observed across multiple years (2.4-11.5% per year, average 8.41%) without significant trends in MIC change over time. Itraconazole and posaconazole demonstrated the lowest MIC distributions (MIC₅₀ ≤ 0.06-0.5 µg/mL) of the azoles against <i>Aspergillus</i> spp. Amongst the <i>A. niger</i> complex, 29.4% (27/92) demonstrated non-wild-type MICs to itraconazole. While the <i>A. nidulans</i> group was less frequent (<i>n</i> = 24), bimodal peaks in MIC/MEC were noted for caspofungin (≤0.06 and 1 µg/mL). Non-<i>Aspergillus</i> molds of significance (Zygomycetes, <i>Fusarium</i> spp., <i>Scedosporium</i> spp., and <i>Lomentospora prolificans</i>) demonstrated variable but increased MICs to antifungal agents as previously described. Our results highlight increased rates of non-wild type MICs for <i>Aspergillus</i> spp. to isavuconazole and voriconazole, which are commonly used antifungal agents in cancer patients. Such AST trends should be closely monitored in populations with frequent antifungal use and encourage increased antifungal stewardship efforts.