Coexistence of Low-Grade Fetal Adenocarcinoma and Adenocarcinoma in situ of the Lung Harboring Different Genetic Mutations: A Case Report and Review of Literature

Low-grade fetal lung adenocarcinoma (L-FLAC) is an exceptionally rare pul- monary tumor, presenting with unclear histological and molecular features. In particular, the potential driver genes of L-FLAC remain elusive. To date, only fi ve reports have documented genetic aberrations in L-FLAC. In the current study, we describe an unusual case of L-FLAC coexisting with adenocarcinoma in situ (AIS) of the lung, harboring different genetic mutations. A 39-year-old non-smoker female patient was referred to our hospital with the chief complaint of dyspnea for 20 days. Chest computed tomography (CT) revealed a - 2.5x1.5x1.5 cm nodule in the right middle lobe, with no mediastinal lymph node enlarge- ment or distant metastases. Thoracoscopic surgery was performed to remove the nodules. Histopathological analysis of the tissue sections, based on fi ndings from immunohistochem- ical staining, con fi rmed a diagnosis of L-FLAC coexisting with AIS of the lung. Next- generation sequencing revealed L-FLAC-based mutations in DICER1 and CTNNB1 , and AIS harboring KRAS mutations. Currently, the patient remains recurrence-free 17 months after the initial diagnosis. This report presents the fi rst case demonstrating the coexistence of L-FLAC and AIS in the same pulmonary nodule, harboring different genetic mutations. Based on the literature review, this is the second reported case of L-FLAC bearing DICER1 mutations.