SESSION TITLE: Lung Cancer SESSION TYPE: Fellow Case Report Posters PRESENTED ON: 10/09/2018 01:15 PM - 02:15 PM INTRODUCTION: Adenosquamous lung cancer (ASLC) comprises only 0.4% to 4.0% of all primary lung cancers and carries the worst prognosis when comparing to individual histology, owing its high mortality to brain metastases as the major cause of death. Our case illustrates the severity and rapidity of such a disease; however it also demonstrates a unique metastatic histological transformation. CASE PRESENTATION: 38 year old Jamaican male with no past medical history presented complaining of worsening right side weakness for 1 month. The ascending hemiparesis started in the right lower extremity and eventually progressed to the right upper extremity sparing the intrinsic muscles of the hand. Reflexes were normal throughout and there were no signs of sensory deficits. Review of systems was positive for night sweats and unintentional weight loss of 5 lbs in the past 2 months. Social history was significant for smoking 20 pack years as well as daily use of marijuana. CT thorax revealed a spiculated nodule in the right upper lobe measuring 1.7 x 1.9 x 2.1 cm with mild superior pleural retraction and right paratracheal lymphadenopathy. CT brain showed large areas of white matter edema in the frontal lobes bilaterally in conjunction with bilateral hypodense cystic masses with the largest measuring 4.2 x 2.5cm with a midline shift of 2.5mm. Left sided craniotomy was performed to resect the cystic frontal lobe tumor. Histology was notable for metastatic squamous cell carcinoma with the following supportive immunohistochemistry: positive CK5, CK6, CK7, P63, and Ki-67. Furthermore, a right upper lobe wedge resection revealed histology positive for adenosquamous carcinoma with lymphovascular invasion and positive mucin stains. EGFR, KRAS, and ALK immunohistochemistry came back negative. Upon discharge, the patient was followed by oncology and only pursued radiation treatment. DISCUSSION: In order to make a diagnosis of ASC, each histological component must make up at least 10% of the tumor. The histology along with the immunochemistry and mucin stain findings is what led us to diagnose the patient with ASC lung carcinoma. The histogenesis of ASC neoplasm has been investigated for many years; however, it is still unclear. The ASC tumor contains two phenotypes with two different lineages, one being columnar cells and the other being squamous cells. The two theories that exist are monoclonality and polyclonality. Polyclonality is described as the theory of the collision of two histologically independent tumors, while monoclonality signifies a single lineage. CONCLUSIONS: ASC lung cancer is known to be invasive with early stage metastasis and a prognosis of 6 month mortality. The histogenesis of this malignancy has long been debated. Our case demonstrates the fact that the metastatic site was only found to be composed of purely squamous cell; therefore, our case supports the polyclonal theory. Reference #1: Min Kong, Jiang Jin, Xiuyu Cai. Characteristics of lymph node mestastasis in resected adenosquamous lung cancer. Medicine (Baltimore). 2017 Dec; 96(48); e8870. Reference #2: Pan Yang, Wei-Lang Li, Jeff-X Zhou. Peritoneum as the sole distant metastatic site on lung adenosquamous carcinoma: a case report. J Med Case Rep. 2017; 11: 274. Reference #3: Jarred Burkart, Konstantin Shilo, Metastatic Squamous Cell Carcinoma Component from an Adenosquamous Carcinoma of the Lung with Identical Epidermal Growth Factor Receptor Mutations. Case Rep Pulonology. 2015; 2015: 283875. DISCLOSURES: No relevant relationships by Artur Alaverdian, source=Web Response No relevant relationships by Theresa Henson, source=Web Response No relevant relationships by Elyana Matayeva, source=Web Response