LUNG NODULE WITH PAPILLARY FEATURES ON BIOPSY: A DIAGNOSTIC DILEMMA

Abstract

SESSION TITLE: Monday Medical Student/Resident Case Report Posters SESSION TYPE: Med Student/Res Case Rep Postr PRESENTED ON: 10/21/2019 02:30 PM - 03:15 PM INTRODUCTION: Papillary adenocarcinoma (PA) is a rare sub type of adenocarcinoma of the lung. It can have histological and immunohistochemistry features like papillary thyroid carcinoma (PTC). We report a case of lung nodule found to have features suggestive of PTC on biopsy. CASE PRESENTATION: A 69-year-old female with a history of COPD and colon cancer presented to the pulmonologist for follow up of a solitary lung nodule in the right upper lobe, which was first diagnosed two years back. It had shown a recent increase in size from 8 mm to 12 mm, with spiculated pattern on imaging. Biopsy of the lung nodule was highly suspicious for PTC, with positive TTF1, papillary features, intranuclear cytoplasmic inclusions, nuclear grooves, negative CK20, CDX2 immunostain. She denied any symptoms of hypo/hyperthyroidism, weight loss, fatigue, cough, dyspnea, neck radiation exposure. She had a 37.5 pack-year smoking history. Family history was non-contributory. Vital signs and physical examination were unremarkable. Thyroid function tests including TSH, fT3, fT4 were within normal limits. With findings suggestive of PTC on biopsy, initial concern was for metastatic disease. Thyroid ultrasound showed 0.7cm cystic nodule in the right lobe, and two solid nodules of 0.9cm, 0.8cm on the left. FNAC of the nodules showed benign pathology. Tumour board was consulted, and they recommended MRI of the neck with contrast which revealed mildly enlarged thyroid with sub centimetric nodules, without lymphadenopathy, making our suspicion for metastatic PTC very low. Ectopic thyroid tissue carcinoma, PA of the lung were now being considered as differentials. Lung biopsy slides were sent to Mayo clinic for a second opinion, which revealed neoplastic cells with lining of papillary structures, with positive immunochemistry for napsin-A and TTF1, and negative for Pax-8, confirming the diagnosis of primary PA. DISCUSSION: PA accounts for 7-12% of lung adenocarcinomas, with a predilection for female smokers. It mimics PTC, as they can have similar histological features of pseudo-inclusions, intra-nuclear grooves. In such cases, immunohistochemistry aids in the diagnosis. Although, our patient had a nodule which morphologically resembled PTC, the history of solitary lung nodule, in the absence of significant findings on imaging and biopsy made the diagnosis of PTC unlikely. CONCLUSIONS: Most common etiology for lung nodule showing papillary features is metastatic disease. The combination of positive TTF1, napsin-A, and negative Pax-8 is a reliable tool to differentiate primary lung adenocarcinoma from metastatic tumors. Understanding the existence of papillary thyroid carcinoma-like primary pulmonary papillary adenocarcinoma will avoid misdiagnosis or unnecessary investigations. Reference #1: Zhu YZ, Li WP, Wang ZY, Yang HF, He QL, Zhu HG, Zheng GJ. Primary pulmonary adenocarcinoma mimicking papillary thyroid carcinoma. J Cardiothoracic Surg. 2013; 17; 8:131 Reference #2: El-Maqsoud NM, Tawfiek ER, Abdelmeged A, Rahman MF, Moustafa AA. The diagnostic utility of the triple markers Napsin A, TTF-1, and PAX8 in differentiating between primary and metastatic lung carcinomas. Tumour Biol. 2016; 37(3):3123-34 Reference #3: Karmakar S, Nath A, Neyaz Z, Agarwal V, Ahsan S. Primary papillary adenocarcinoma of lung: Report of two cases. Lung India. 2017; 34(3):299-302 DISCLOSURES: No relevant relationships by Shujaa Faryad, source=Web Response No relevant relationships by Pallavi Pradeep, source=Web Response