Clinical features of primary lung cancer presenting as pulmonary consolidation mimicking pneumonia

Objectives: It is well recognized that lung cancer can present as parenchymal infiltration mimicking pneumonia on chest X-ray films or computed tomography images. Such cancers can be misdiagnosed as inflammatory lung diseases, delaying accurate diagnosis. Methods: We retrospectively reviewed nine consecutive lung cancer patients who presented with pulmonary consolidation mimicking pneumonia at their initial examinations between January 2012 and December 2014 and analyzed their clinical courses and radiological and pathological findings. Results: The nine patients (six men) were aged 47 to 86 years (median 75 years). Four were smokers or exsmokers. In all cases, radiological findings included parenchymal opacification with air bronchograms; in some cases, parenchymal consolidation was associated with volume loss and traction bronchiectasis and located in the subpleural zone. Ground glass opacity or tree-in-bud appearance (suggesting aerogenous metastasis) also sometimes accompanied the consolidation. In all cases, biopsies revealed adenocarcinoma (including three cases of invasive mucinous adenocarcinoma). Neither EGFR gene mutation nor ALK gene rearrangement were found; however, KRAS mutation was identified in five cases. Although lung infiltrations had been recognized for two or more months in some cases, no previous biopsies had been performed. Furthermore, in three cases, initial bronchoscopic examination had failed to diagnose malignancy. None of these patients responded to chemotherapy and four cases died within 6 months of diagnosis. Conclusion: Diagnosis of lung cancer presenting as lung consolidation mimicking pneumonia is difficult and often delayed. The prognosis is poor because of delayed diagnosis and poor response to chemotherapy.