Stromal micropapillary predominant lung adenocarcinoma: A rare histological phenotype with poor prognosis

An extremely rare case of stromal micropapillary predominant lung adenocarcinoma is presented in this study. A 70‐year‐old woman visited our hospital because of an abnormal shadow on chest X‐ray. Chest computed tomography revealed a nodule in the left lower lobe and a mass in the left upper lobe. She underwent an exploratory thoracotomy owing to the suspicion of advanced lung cancer. Pathological examination of the left lower lobe nodule revealed tumour cells with more than half the tumour cells showing stromal micropapillary pattern (SMP), consisting of tumour cells invading the fibrotic stroma. In general, micropapillary adenocarcinomas in the lung form an aerogenous micropapillary pattern (AMP), in which tumour cells float in alveolar spaces. Because the prognosis of SMP lung adenocarcinomas is known to be worse than that of AMP lung adenocarcinomas and have a high frequency of epidermal growth factor receptor mutations, the discrimination of SMP from AMP is important for both pathologists and clinicians.