Mucinous Adenocarcinoma of the Lung Diagnosed on Sputum Cytology Initially Mimicking as Pneumonia

Abstract Introduction: Mucinous adenocarcinoma is a rare lung cancer that can be misdiagnosed initially as infectious or aspiration pneumonia on imaging. Typical computed tomography (CT) findings indicative of mucinous adenocarcinomas, such as consolidations and opacities, can mimic those of pneumonia. We present a case in which mucinous adenocarcinoma of the lung was initially diagnosed as pneumonia. Case Presentation A 70-year-old man with history of bullous emphysema who initially presented to the pulmonary clinic with productive cough and dyspnea. Prior to his presentation, he went to emergency department a month ago for similar symptoms. CT Chest was performed, which showed ground-glass opacities in the right middle and lower lobes (Figure 1a). Patient completed seven days of antibiotics prior to his clinic presentation. In view of no improvement after antibiotics, it was decided to perform bronchoscopy. He underwent a bronchoscopy with bronchoalveolar lavage with negative cultures, including mycobacterial cultures. Cytology revealing acute inflammation and atypical cells. Patient completed another round of antibiotics after the bronchoscopy. However, three weeks after bronchoscopy, patient presented to emergency department with increasing sputum production (bronchorrhea) and shortness of breath requiring supplemental oxygen. Patient was bringing up approximately 500 ml/day of clear white sputum. Laboratory workup was unremarkable. A repeat CT imaging showed worsening right lung ground glass opacities with right upper lobe dense consolidation (Fig 1b). A speech and swallow evaluation with an esophagogram was negative for any aspiration. Patient was reluctant to undergo bronchoscopy with possible cryo-biopsy of the lung for definitive diagnosis. As patient was unwilling for lung biopsy, his sputum collected over 12 hours (approximately 200 ml) were sent for malignant cell examination. Pathological examination of sputum revealed malignant cells consistent with mucinous adenocarcinoma. Discussion Mucinous adenocarcinoma of the lung is uncommon, difficult to distinguish on imaging from infectious pneumonia, and has generally poor prognosis in the absence of targetable molecular mutations. The present case highlights the utility of basic noninvasive procedure as diagnostic tool which is often forgotten and not practiced while investigating lung cancer diagnosis. To the best of our knowledge this is one of very few cases of mucinous adenocarcinoma of the lung diagnosed on sputum sample. Due to its low incidence rates, survival data on mucinous adenocarcinoma patients is scarce and often contraindicatory.