Genetic mutations-based criteria to distinguish multiple primary lung cancers from intrapulmonary metastasis in patients with lung tumors.

e21038 Background: Patients with multiple primary lung cancers (MPLC) and intrapulmonary metastasis (IPM) are considered as different clinical stages and require different treatment strategies. At present, the molecular identification criteria employed for distinguishing MPLC and IPM still need to be improved. Therefore, there is an unmet medical need in regards to a diagnostic standard that could effectively distinguish MPLC from IPM. Methods: Between December 2014 and April 2020, a total of 35 patients, with more than two lung lesions, were selected and divided into a training cohort (N = 22) and a validation cohort (N = 13). Imaging, anatomical evidence, pathological results, and histological examinations of the primary tumor, as well as histological subtypes, were used to differentiate MPLC from IPM. Genomic profiles obtained using a targeted sequencing with 450 cancer-related genes panel were analyzed. Modified diagnostic criteria for MPLC and IPM were established based on Martini and Melamed criteria, as well as molecular profiles. Results: We developed interpretation criteria using a flowchart that distinguishes MPLC from IPM, as follows: 1) MPLC can be determined using the following aspects: no common mutations are present; one lesion has no mutations (tumor = 2); two common high frequency driver gene mutations are present, or one driver gene mutation and one rare mutation comprising the p53 mutation are present; and only one common mutation is present. 2) IPM can be determined using the following aspects: one driver gene mutation and one rare mutation comprising the p53 mutation (concordance rare ≥ 50%) are present; two driver gene mutations (concordance rare ≥ 60%) are present; all mutations are common; and more than three common mutations are present. 3) Undetermined results are based on the following aspects: no mutations in one tumor are present (tumor > 2); no mutations are identified in all tumors; or two rare mutations are present. Undetermined patients were identified by combining histological identifications. Subsequently, to verify the criteria, 13 patients were recruited as a validation cohort. Eight MPLC and 5 IPM patients were identified, and the results were 100% consistent with independent imaging and pathological diagnoses. Conclusions: In this work, we proposed more comprehensive and detailed molecular identification criteria for MPLC and IPM, and it suggested that genetic alterations may be an effective method for diagnosing MPLC and IPM. We also determined that NGS may be a useful tool for assisting with differential diagnoses. Key words: Multiple lung cancer, Multiple primary lung cancer, Intrapulmonary metastasis, Next-generation sequencing, molecular classification.