ABPM secondary to Saccharomyces cerevisiae mimicking lung cancer in an immunocompetent patient

Summary We present a case of allergic bronchopulmonary mycosis due to Saccharomyces cerevisiae mimicking lung cancer in an immunocompetent woman in her early 70s. She had a 6-week history of dry cough and chest X-ray changes concerning for malignancy. CT initially suggested primary lung cancer. Blood tests showed eosinophilia (4.2×10⁹/L) and moderately elevated total IgE (296 IU/mL). Aspergillus precipitins were mildly raised (140 mgA/L), but no Aspergillus -specific growth or serological sensitisation was found. She developed acute respiratory distress requiring emergency cardiothoracic intervention for near-total collapse of the left lung caused by occlusion of the left main bronchus, initially presumed malignant. Bronchoscopy revealed a large mucus plug obstructing the bronchus, which was removed, with no visual tumour. Bronchial washings showed reactive bronchial epithelium without malignancy, and sputum cultures taken during bronchoscopy identified Saccharomyces cerevisiae .