The relationship between organising pneumonia and invasive mould disease in patients with haematologic malignancy

Background Organising pneumonia (OP) is reported in patients with haematologic malignancy suspected of having invasive mould disease, yet little is known about this relationship. Objective To investigate molecular evidence of invasive mould pneumonia in paraffin‐embedded lung tissues from histologically diagnosed OP patients with suspected invasive mould pneumonia. Patients/Methods Patients with haematologic malignancy suspected to have invasive pulmonary mould disease who underwent lung biopsy at a tertiary hospital, Seoul, South Korea, between 2008 and 2020, were retrospectively reviewed. To find molecular evidence of fungal infection, PCR assay was used to detect Aspergillus‐ and Mucorales‐specific DNA within OP lung tissue sections. Results Forty‐seven patients with suspected invasive mould pneumonia underwent lung biopsy and 15 (32%) were histologically diagnosed as OP without any evidence of fungal hyphae. Of these 15 patients, 3 (20%) received allogenic haematopoietic stem cell transplantation prior to developing OP. Before biopsy, 2 and 13 patients had probably and possible invasive mould disease, respectively. The median antifungal treatment length was 81 [8–114] days, and the median steroid treatment dosage was 0.35 mg/kg/day for 36 days (methylprednisolone equivalent doses), respectively. After biopsy, three patients with possible invasive mould infection revealed probable invasive pulmonary aspergillosis. From the 15 paraffin‐embedded lung tissues, 6 (40%) exhibited positive PCR assay results for detecting Aspergillus‐ and Mucorales‐specific DNA. Conclusions More than one third of OP cases in patients with suspected invasive mould pneumonia exhibited molecular evidence of invasive mould infection by fungus‐specific PCR in lung tissues, likely associated with concurrent or prior fungal infection.