Tumorlet is a disease rarely diagnosed in clinical practice. It is characterized by pulmonary neuroendocrine cell (PNEC) proliferation which invades the bronchiolar basement membrane and forms nodules with a diameter smaller than 5 mm. Case report: 72-year-old female patient was suffered for many years from progressive dyspnea and coughing with evidence of pulmonary fibrosis on high resolution computed tomography (HRCT). As a result of a lung biopsy, based on immunohistochemical tests, a 2 mm cluster of neuroendocrine cells (NEC) was found and it was diagnosed as tumorlet. Due to a long-term, insidious progress of the disease, as well as sex and age of the patient, the case emphasizes that differential diagnosis should include tumorlet as well as diffuse idiopathic neuroendocrine cell hyperplasia (DIPNECH) as a more extensive manifestation of neuroendocrine cell proliferation in the respiratory tract.
Keywords: DIPNECH; IPF; dyspnea; tumorlet.