SESSION TITLE: Medical Student/Resident Lung Cancer Posters SESSION TYPE: Med Student/Res Case Rep Postr PRESENTED ON: October 18-21, 2020 INTRODUCTION: Multiple primary lung cancers (MPLC) are a rare occurrence and have 2 forms – synchronous (sMPLC) and metachronous (mMPLC). The sMPLCs are physically distinct with different histological subtypes. If they are the same subtype, they must be in different lobes of the lung, originating from carcinoma in situ, and no tumor in common lymphatics and extrapulmonary metastases. The mMPLCs tumors must be histologically different or if they are histologically identical, there must be a >2 year cancer free interval, originate from carcinoma in situ, and second cancer must be in a different lobe or lung with no carcinoma in the common lymphatics and no extrapulmonary metastases. mMPLC is common and secondary to treatment of initial lesions. Tobacco smoke may also create a “field effect” in which multicentric lung cancers manifest more frequently. CASE PRESENTATION: A 66-year-old female presented for follow up of sMPLC Stage IB left upper lobe adenocarcinoma/Stage IA right middle lobe squamous cell carcinoma. Patient was treated in 2015 via left upper lobectomy and right middle lobe pulmonary wedge resection. Patient history includes 40-pack-years of smoking, COPD, and continued smoking after treatment of prior sMPLC. Surveillance chest CT showed increase in size of subcarinal lymph node and right lymph node conglomerate encasing the right upper lobe pulmonary artery, consistent with metastasis. Fine needle aspiration of level 4R lymph nodes revealed cells clusters with nuclear molding, high nuclear to cytoplasmic ratio, inconspicuous nuclei, minimal cytoplasm, and crush artifacts. Immunohistochemically tumor cells were positive for TTF-1 and synaptophysin, and negative for P40 – confirming diagnosis of small cell carcinoma. DISCUSSION: Small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC) are known to be linked with tobacco, creating a “field effect” that promotes the possibility of MPLCs. NSCLC include adenocarcinoma and squamous cell carcinoma (SCC). SCLC and NSCLC are differentiated based on morphology and immunohistochemical staining, the results of which confirmed diagnosis of small cell carcinoma and thus qualified as mMPLC in our case. Treatment of mMPLC is often surgical resection, however, feasibility must be assessed based on pulmonary reserve. Limited resections should be attempted in all cases as segmentectomies have similar outcomes to lobectomies in terms of recurrence-free survival, notably in tumors under 3 cm. CONCLUSIONS: In patients with a history of MPLC associated with smoking, physicians should be cognizant of additional malignancies different from the original lesion subtype. Biopsy and histopathology are the gold standard for diagnosis. Surgery is the standard treatment in MPLC, but clinicians should assess for sufficient pulmonary reserve to ensure viability. Reference #1: Chen C, Huang X, Peng M, Liu W, Yu F, Wang X. Multiple primary lung cancer: a rising challenge. Journal of thoracic disease. 2019; 11(Suppl 4):S523-S536. Reference #2: Chen TF, Xie CY, Rao BY, et al. Surgical treatment to multiple primary lung cancer patients: a systematic review and meta-analysis. BMC surgery. 2019; 19(1):185. Reference #3: Jiang L, He J, Shi X, et al. Prognosis of synchronous and metachronous multiple primary lung cancers: systematic review and meta-analysis. Lung cancer (Amsterdam, Netherlands). 2015; 87(3):303-10. DISCLOSURES: No relevant relationships by jayanth keshavamurthy, source=Web Response No relevant relationships by Diana Kozman, source=Web Response No relevant relationships by Samantha Mattox, source=Web Response No relevant relationships by Rohit Munagala, source=Web Response No relevant relationships by Nikhil Patel, source=Web Response No relevant relationships by Kanwar Singh, source=Web Response No relevant relationships by Asad Ullah, source=Web Response