Lung adenocarcinoma coexisting with diffuse idiopathic pulmonary neuroendocrine cell hyperplasia manifesting as multiple pulmonary nodules: A case report.

Diffuse idiopathic pulmonary neuroendocrine cell hyperplasia (DIPNECH), a rare condition, is characterized by pathological proliferation of neuroendocrine cells. Some of them are localized to the airway mucosa, and others locally infiltrate to form tumorlets and nodules. Here, we present a patient with lung adenocarcinoma accompanied by DIPNECH, making the latter difficult to distinguish from multiple pulmonary metastases. The patient, a 72-year-old Japanese woman, was diagnosed as having stage IVA lung adenocarcinoma because she had multiple nodules in both lungs. Mutation of epidermal growth factor receptor gene having been found in the primary tumor, treatment with osimertinib was started. This resulted in shrinkage of the primary tumor, but not the multiple pulmonary nodules. To determine whether these lung nodules were indeed lung metastases, we performed right upper lobectomy with lymphadenectomy and wedge resection of the right lower lobe. On pathological examination, the primary tumor was diagnosed as invasive adenocarcinoma, whereas the multiple pulmonary nodules were diagnosed as DIPNECH manifesting as tumorlets. Therefore, the final diagnosis was stage IA1 lung adenocarcinoma accompanied by DINPECH. The patient had no recurrences 1 year after the operation without any additional treatment. This is a rare case of lung adenocarcinoma accompanied by DIPNECH presenting as multiple pulmonary nodules. DIPNECH should be included in the differential diagnosis of multiple pulmonary nodules.