NOT EVERY PET POSITIVE MASS IS CANCER

Abstract

TOPIC: Lung Pathology TYPE: Fellow Case Reports INTRODUCTION: Tuberculosis (TB) is well known as a diagnostic chameleon.1 Both symptomatic and asymptomatic cases of TB can mimic lung cancer with cough, hemoptysis, and weight loss common for both diseases. Many radiological findings on CT imaging and PET avidity can occur with both.2 We present a patient who presented with abnormal imaging who was ultimately diagnosed with pulmonary TB. CASE PRESENTATION: A 55-year old man presented to pulmonary clinic with an enlarging right upper lobe (RUL) mass. The mass was first noted a year prior while being evaluated for anemia and lymphadenopathy thought to be autoimmune. Despite steroids and antibiotics, the mass increased in size. He also had diabetes, tobacco use, and treated latent TB (positive QuantiFERON gold). To evaluate the RUL mass, he had a diagnostic bronchoscopy with transbronchial biopsy which showed scant non-necrotizing granulomas but negative fungal/AFB stains and cultures, and no evidence of malignancy. Given lack of certainty, he underwent navigational bronchoscopy with repeat bronchial wash, and a biopsy of the right upper lobe mass was obtained. The MTB PCR was positive and pathology showed necrotizing granulomas. Despite negative fungal/AFB stains and cultures, the positive PCR and caseating granulomas were consistent with pulmonary TB and he was promptly started on rifampin, isoniazid, pyrazinamide, and ethambutol with pyridoxine. With treatment of TB, both his symptoms and anemia resolved. DISCUSSION: While a growing, PET-avid lung mass in a patient with tobacco exposure is most likely malignant, a broad differential, including granulomatous diseases, should be considered. Of note, some malignancies may co-exist with granulomatous infections, including intra-pulmonary lymphoma or mucinous adenocarcinoma, requiring careful attention to follow-up imaging and a low threshold for repeat biopsies. Repeat navigational bronchoscopy with bronchial wash confirmed the presence of necrotizing granulomas and a positive PCR test, sparing the patient from a surgical biopsy. CONCLUSIONS: Differentiating pulmonary TB from malignancy based on clinical and radiological evaluation can be challenging. Both diseases can present with similar symptoms and parenchymal infiltrates with high metabolic activity on the 18-FDG-PET. The presence of necrotizing granulomas on transbronchial biopsy along with positive PCR testing confirms the diagnosis, but careful attention to follow-up imaging with treatment is warranted. REFERENCE #1: Lang S, Sun J, Wang X, et al. Asymptomatic pulmonary tuberculosis mimicking lung cancer on imaging: A retrospective study. Exp Ther Med. 2017;14(3):2180-2188. doi:10.3892/etm.2017.4737 REFERENCE #2: Hammen I. Tuberculosis mimicking lung cancer. Respir Med Case Reports. 2015;16:45-47. doi:10.1016/j.rmcr.2015.06.007 DISCLOSURES: no disclosure on file for George Cheng; No relevant relationships by Brinda Desai, source=Web Response No relevant relationships by Russell Miller, source=Web Response No relevant relationships by Matthew Nobari, source=Web Response No relevant relationships by Rebecca Sell, source=Web Response