255. Breakthrough Mucormycosis (BT-MCR) on Antifungals Having Mucorales Activity Portrays Worse Prognosis compared with BT-MCR on Mold-Active Antifungals with no Mucorales Activity

BACKGROUND: BT-MCR is known to develop in the setting of agents having Aspergillus but no Mucorales activity. However, BT-MCR can occur even with the use of antifungals having with Mucorales activity in patients with hematologic malignancies and or stem cell transplant (HM). METHODS: We reviewed the records of HM patients treated for MCR (1994 to 2019) at MD Anderson Cancer Center. We identified patients with BT-MCR on antifungals having Mucorales activity: posaconazole (POSA), isavuconazole (ISA), and amphotericin B (AMB) (group A), and patients with BT-MCR on agents having Aspergillus but no Mucorales activity: voriconazole (VRC), itraconazole (ITZ), echinocandins (group B). BT-MCR was defined as MCR diagnosis (dx) after ≥7days (d) of antifungal use. The primary outcome was 42d mortality after the BT-MCR dx. Chi-square or Fisher’s exact test was used for categorical variables and Wilcoxon rank-sum test used for continuous variables. Cox regression model was used to evaluate the independent variables on outcome. RESULTS: We identified 11 patients in group A (3 POSA, 5 ISA, 3 AMB) and 81 patients in group B (61 VRC, 13 echinocandins, 7 ITZ). Both groups were not different in terms of age, sex, underlying HM (AML/MDS in 100% vs. 88% in groups A and B, respectively), status of HM (active disease in 82% vs. 67%), prior stem cell transplant (45% vs. 54%) or GvHD (80% vs. 84%), neutropenia at dx (55% vs. 42%), prior receipt of >600 mg of prednisone (45% vs. 41%) or ICU at MCR dx (36% vs. 26%). Similarly, Mucorales species (Rhizopus spp. in 55% vs. 49%) and type of infection (sino-pulmonary in 73% vs. 68%) were no different between the groups. However, both d42 (82% vs. 46%, P = 0.025) and d84 (100% vs. 60%, P = 0.007) mortality was worse in group A. Similarly, median time to death was faster in patients in group A (26d, range 7-80d), vs. group B (42d, range 4–3146d, P = 0.031). Kaplan–Meier analysis showed a similar difference (Figure 1). In multivariate analysis, neutropenia (P = 0.038) and ICU at dx (P = 0.002) were independent factors on day 42d mortality in all 92 patients with prior Mucorales–active antifungals showing a trend associated with poor outcome (P = 0.17). CONCLUSION: BT-MCR on agents having Mucorales activity is a marker of poor prognosis in HM patients. Early use of investigational immunotherapy and salvage antifungal chemotherapy studies is needed in that subgroup of patients. [Image: see text] DISCLOSURES: All authors: No reported disclosures.