B80-5-40 Metastatic Mimic: Diffuse Idiopathic Pulmonary Neuroendocrine Cell Hyperplasia Masquerading as Breast Cancer Metastases

Abstract Pulmonary nodules are perhaps the most common incidental thoracic imaging finding in the modern era of CT imaging. Most commonly benign, they may also represent infection, inflammation (particularly granulomatous), vascular abnormalities, or malignancy among many other causes. Patient risk factors are critical to consider when creating a diagnostic and therapeutic plan. We present a case of incidental pulmonary nodules in an asymptomatic patient with a history of breast cancer. A 40-year-old female presented to the emergency department after a motor vehicle accident, where CT chest identified numerous bilateral subcentimeter pulmonary nodules that had slowly increased in size and quantity over the past eight years. Her medical history was notable for stage one invasive ductal carcinoma adjacent to ductal carcinoma in situ of the left breast that was treated with bilateral mastectomy, and was now felt to be in remission. Subsequent PET-CT demonstrated borderline metabolic activity in the lung nodules (maximal SUV 2.4) with maximum nodule size 8 mm. She denied weight loss, fatigue, night sweats, or fevers. The patient later developed dyspnea on exertion with increased albuterol use. Navigational bronchoscopy with transbronchial cryobiopsies of a right upper lobe nodule was performed, with pathology demonstrating neuroendocrine cell proliferation. She was diagnosed with a well-differentiated, grade 2 neuroendocrine tumor vs carcinoid tumorlet of the right upper lobe. In the context of her imaging, a diagnosis of Diffuse Idiopathic Pulmonary Neuroendocrine Cell Hyperplasia (DIPNECH) was made. DIPNECH is a very rare pulmonary disease characterized by generalized hyperplasia of pulmonary neuroendocrine cells. These cells can remain confined to the mucosa, form small tumorlets, or develop into well-differentiated neuroendocrine tumors. Patients may be asymptomatic or present with respiratory symptoms, particularly wheezing. Diagnosis is typically made based on imaging showing lung nodules, biopsy results showing neuroendocrine cell hyperplasia, and fitting symptoms. Our patient was managed with conservative management and serial imaging. This case demonstrates the need to keep differential diagnoses broad for pulmonary nodules in a patient with a history of cancer to resist anchoring bias. Furthermore, DIPNECH may present with neither pulmonary nor classic carcinoid symptoms, and maintaining a high clinical suspicion is necessary to ensure diagnostic precision. This abstract is funded by: None