A 53 year old woman with a 40 pack year smoking history consulted her physician for a chronic cough.A chest x-ray disclosed an infiltrate in the right middle lobe.She was treated with two courses of antibiotics,but six weeks later,the infiltrate had not improved.A bronchoscopic biopsy was performed,a representative section of which is shown in the accompanying photomicrograph.Which one of the following is the best diagnosis?

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Bronchioloalveolar carcinoma is an unusual malignancy that does not present as a distinct mass in the lung,and is often mistaken for pneumonia,as suggested in the clinical vignettEThe microscopic picture is pathognomonic,with large,often mucin-secreting cells lining the alveolar septaEThe tumour is classified as an adenocarcinoma,but bronchioloalveolar carcinoma is a more specific term for this histological pattern.

A 53 Year Old Woman with a 40 Pack Year