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

## TL;DR

This study examines antifungal resistance in mold isolates from cancer patients, finding rising resistance to commonly used drugs like isavuconazole and voriconazole.

## Contribution

The study provides new data on antifungal susceptibility trends in cancer patients, highlighting resistance patterns in Aspergillus species.

## Key findings

- Isavuconazole showed high non-wild-type MIC rates in multiple Aspergillus species.
- A. fumigatus resistance to voriconazole remained low but stable over time.
- Itraconazole and posaconazole had the lowest MIC distributions against Aspergillus spp.

## Abstract

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 Aspergillus spp.) from cancer patients. Based on published Clinical and Laboratory Standards Institute guidelines, isavuconazole had notably high rates of non-wild-type MICs for A. fumigatus (19.6%), A. flavus/oryzae (34.8%), A. niger complex (26.1%), and A. terreus complex (8.33%). Persistent low baseline resistance of A. fumigatus 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 Aspergillus spp. Amongst the A. niger complex, 29.4% (27/92) demonstrated non-wild-type MICs to itraconazole. While the A. nidulans group was less frequent (n = 24), bimodal peaks in MIC/MEC were noted for caspofungin (≤0.06 and 1 µg/mL). Non-Aspergillus molds of significance (Zygomycetes, Fusarium spp., Scedosporium spp., and Lomentospora prolificans) demonstrated variable but increased MICs to antifungal agents as previously described. Our results highlight increased rates of non-wild type MICs for Aspergillus 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.