SESSION TITLE: Lung Cancer 1 SESSION TYPE: Med Student/Res Case Rep Postr PRESENTED ON: 10/09/2018 01:15 PM - 02:15 PM INTRODUCTION: Adenocarcinoma in situ (AIS) of the lung usually presents on computed tomography (CT) of the chest as solid nodules, although part-solid or groundglass nodules are also often seen. In the case of cavitary lesions on CT in combination with nodular opacities, the diagnosis of Mycobacterium avium complex (MAC) infection is more readily considered. Herein is a case in which AIS with concurrent MAC infection presented on CT with multifocal cavitary lesions. CASE PRESENTATION: A 60-year-old Caucasian female with a history of former tobacco use presented with chronic cough productive of white sputum for four months as well as dyspnea on exertion. She was diagnosed on two separate occasions with pneumonia thirteen and three months prior to presentation. Evaluation of her cough included chest CT, which revealed dense consolidation with air bronchograms and widespread interstitial infiltration with groundglass opacities highlighting numerous cysts in the right upper lobe; a 6-cm cavitary lesion in the superior segment of the right lower lobe; and bilateral nodularity with both groundglass and cavitary components in a centrilobular, non-hematogenous distribution in the central lung zone regions. The clinical presentation and the radiologic findings were initially concerning for MAC infection. Bronchoscopy with transbronchial lung cryobiopsy (TBLC) was performed to confirm the diagnosis. However, cytology revealed malignant glandular cells consistent with adenocarcinoma, and surgical pathology revealed moderately-differentiated, non-mucinous neoplastic epithelium with papillary architecture consistent with AIS. Sputum smear initially revealed no acid-fast bacilli, but three weeks later cultures grew Mycobacterium avium-intracellulare. DISCUSSION: The pathology results of this patient are consistent with a diagnosis of lepidic-predominant, non-mucinous adenocarcinoma, which has rarely, if ever, been shown to present with cavitary lesions. In contrast, MAC infections routinely exhibit multiple small nodules and fibrocavitary lesions. In addition to radiologic evidence, the patient’s demographics and clinical presentation gave further reason to suspect a diagnosis of MAC infection, so the initial diagnosis of adenocarcinoma in situ was unexpected. Because diagnostic criteria for MAC infection includes radiologic evidence and bronchial washing, biopsy might not always be considered to rule out malignancy, especially with cavitation evident on CT scan. However, without biopsy, the significant diagnosis of adenocarcinoma could be missed. It is also notable to mention that it is necessary to follow up on sputum culture results that could modify treatment if resulted positive. CONCLUSIONS: When considering MAC infection as a diagnosis for cavitary lesions, it may be appropriate to consider biopsy of lesions to rule out malignancy, especially if suggested by the clinical presentation. Reference #1: Austin J, et al. Radiologic Implications of the 2011 Classification of Adenocarcinoma of the Lung. Radiology. 2013;266(1):62-71. Reference #2: Field S, Fisher D, Cowie R. Mycobacterium Avium Complex Pulmonary Disease in Patients Without HIV Infection. Chest. 2004;126(2):566-581. Reference #3: Travis W, et al. International Association for the Study of Lung Cancer/American Thoracic Society/European Respiratory Society International Multidisciplinary Classification of Lung Adenocarcinoma. Journal of Thoracic Oncology. 2011;6(2):244-285. DISCLOSURES: No relevant relationships by Andrew Astin, source=Web Response No relevant relationships by Ezmin George, source=Web Response No relevant relationships by Jeff Hon, source=Web Response No relevant relationships by Vikas Pathak, source=Web Response No relevant relationships by Christine Zhou, source=Web Response