A 55-year-old female was referred to the pulmonology outpatient department with a history of a persistent productive cough of 'pink' sputum for the preceding 12 months. During this time, she also developed progressively worsening dyspnoea and had grade 3 dyspnoea on the modified Medical Research Council scale at the time of presentation to the clinic. No other respiratory symptoms such as wheezing or chest pain were reported and she did not have any constitutional symptoms of fever, night sweats or weight loss. She had no history of any childhood respiratory illnesses nor did she have any history of previous tuberculosis. The patient never smoked and maintained sober habits. Her family history was non-contributory, and she was employed as a domestic worker with no significant exposures that she could recall. She had hypertension and was on chronic medication that included spironolactone, furosemide, amlodipine, aspirin, simvastatin and oestrogen replacement therapy. She previously underwent hysterectomy for abnormal uterine bleeding and no malignancy was detected at the time. 
 She was treated with a 7-day course of amoxicillin-clavulanic acid for supposed community-acquired pneumonia at a local hospital prior to referral. Sputum for microscopy, culture and sensitivity during this time did not yield any pathogens. The result of a tuberculosis GeneXpert test was negative, but Mycobacterium tuberculosis culture or investigations for atypical pathogens were not done. Blood tests showed a white cell count of 7.3 x 109 /L, haemoglobin level of 13.6 g/dL, platelet count of 267 x 109 /L, C-reactive protein level of 21 mg/L and she tested negative for HIV. Although a chest radiograph performed at the local hospital was described as revealing 'extensive opacification of the left lung', the image was not presented at the clinic and thus could not be reviewed. In view of her poor response to treatment and blood results that were not in keeping with infection, she was referred to us for further evaluation 
 On clinical examination, she was obese with a body mass index of 48.24 kg/m2 . Her blood pressure was 120/80 mmHg, pulse rate was 72 beats per minute (bpm), respiratory rate was 15 breaths  per minute and oxygen saturation was 93% measured by pulse oximetry while breathing room air at rest. Arterial blood gas testing was not performed. On respiratory examination, her trachea was centrally situated, but she had dullness to percussion and bronchial breathing of the whole of the left hemithorax, while she had normal percussion and vesicular breath sounds on the right. The rest of the clinical examination was within normal limits. A chest X-ray image at the time of initial assessment revealed complete opacification of the left lung with associated air bronchogrammes noted in the left perihilar region (Fig. 1). Chest computed tomography analysis confirmed dense consolidation of the left lung with no evidence of atelectasis or pleural effusion (Fig. 2).   In view of the clinical problem of a non-resolving pneumonia, the differential diagnoses included atypical pneumonia, non-tuberculous mycobacterial disease, primary lymphoma of the lung and slow-growing primary lung neoplasms. Flexible bronchoscopy was therefore performed to  obtain respiratory specimens for further analysis. Inspection of the tracheobronchial tree revealed an excessive amount of watery sputum in the airways in keeping with bronchorrhea. Bronchoalveolar lavage specimens from the left upper lobe were sent for microscopy, culture and polymerase chain reaction (PCR) tests for Mycobacterium tuberculosis, Pneumocystis jirovecii, Mycoplasma pneumoniae and Chlamydia pneumoniae. All PCR tests were negative. Flow cytometry of bronchoalveolar lavage fluid found a normal ratio of CD4:CD8 cells, in keeping with a reactive T-cell response. Transbronchial lung biopsies, however, revealed tumour tissue with the appearance of a well-differentiated mucus-secreting adenocarcinoma with lepidic features (Fig. 3).  Immunohistochemical staining for cytokeratin 7 (CK7), thyroid transcription factor-1 (TTF-1) and napsin A were positive, while staining for CK20 was negative. A final diagnosis of invasive mucinous adenocarcinoma (previously known as bronchioloalveolar carcinoma) was therefore established.
Chest computed tomography image confirming consolidation of the left lung.