BackgroundThe number of publications on the invasive fungal diseases caused by rare pathogens (rare IFD) after HSCT and chemotherapy is limited. MethodsFrom 2008 to 2017 in R. Gorbacheva Memorial Institute of Children Oncology, Hematology and Transplantation (CIC725) have been performed 2738 HSCT including 1845 allogeneic (allo-HSCT) and 893 autologous HSCT (auto-HSCT). During the observation period 40 probable and proven rare IFD (EORTC/MSG 2008 criteria) cases were diagnosed in children and adults with hematological malignances and non-malignant hematological diseases after allo-HSCT (n=30), auto-HSCT (n=2), and chemotherapy (n=8). The median follow up time for rare IFD cases was 3 months; for survivors – 30 months. ResultsIncidence of rare IFD in HSCT recipients was 1,5%, it was higher after allo-HSCT (1,6%) than auto-HSCT (0,2%) (p<0,01). In 8 patients, this complication developed after CT and 4 of them proceed to allo-HSCT. The most frequent underlying diseases were ALL (33%) and acute AML (30%). The median time of onset of rare IFD after allo-HSCT - 104 (21-1057) days, auto-HSCT – 138 (60-216), after start of CT – 161 (79-189). Etiology of rare IFD was identified by culture in 65% cases: Rhizopus spp. – 27%, Paecilomyces spp. – 7%, Fuzarium spp. – 5%, Malassezia furfur – 5%, Trichosporon asahii – 3%, Scedosporium apiosperium – 2%, Scopulariopsis gracilis – 2%, Rhizomucor pusillus – 2%, Lichtheimia corymbifera – 2%, mix rare IFD with Rhizopus spp. + Paecilomyces spp. – 5%, Paecilomyces spp. + Fuzarium spp. – 5%. 35% cases were diagnosed by microscopy. Antifungal therapy was used in all patients: lipid amphotericin B (L-AmB) – 30%, L-AmB + caspofungin – 22,5%, voriconazole – 17,5%, posaconazole (posa) – 12,5%, L-AmB + posa – 10%, and echinocandins – 7,5%. Overall survival at 12 weeks from the diagnosis of rare IFD was 50%. The 12-weeks overall survival was better in patients after CT and auto-HSCT (80%) than allo-HSCT (42%), p=0,048. ConclusionsThe incidence of rare IFD in HSCT recipients was 1,5%. Rare IFD is a late complication after chemotherapy and HSCT and usually develops after or in combination with invasive aspergillosis. Higher incidence and worst prognosis rare IFD is observed in allo-HSCT recipients. Legal entity responsible for the studyThe authors. FundingHas not received any funding. DisclosureAll authors have declared no conflicts of interest.