Early-Stage High-Grade Fetal Lung Adenocarcinoma With <i>KRAS</i> Mutation: A Rare Presentation and Literature Review

Introduction Fetal lung adenocarcinoma is a rare malignant lung tumor, constituting about 0.1% to 0.5% of primary lung tumors. It is categorized into two types based on histopathological and clinical differences: low-grade and high-grade types. The primary distinction is the formation of morula bodies and β-catenin, P53 expression. High-grade fetal lung adenocarcinoma is more common in middle-aged to elderly men with heavy smoking history; it is highly malignant and often diagnosed with regional lymph node or distant metastasis. Recent literature mainly consists of case reports, focusing on advanced-stage high-grade type, with few reports concerning early-stage high-grade type. Case Report This article reviews the treatment journey of a rare early-stage high-grade fetal lung adenocarcinoma patient. The patient was a non-smoking elderly woman with no respiratory symptoms. A chest CT scan showed a nodule in the lower left lung, with normal tumor markers. Single-port thoracoscopic left lower lung wedge resection was performed, and intraoperative frozen pathology indicated invasive lung adenocarcinoma, leading to lobectomy and mediastinal lymphadenectomy. Postoperative pathology identified high-grade fetal lung adenocarcinoma, with pathological stage pT1bN0 IA2. We present the first report of early-stage high-grade fetal lung adenocarcinoma with KRAS mutation. At 17-month follow-up the patient remains disease-free without adjuvant therapy. Conclusions Diagnosing fetal lung adenocarcinoma, an independent subtype of lung adenocarcinoma, relies on pathological evaluation, and the standard treatment is surgical resection. Since this disease is rare, early-stage high-grade fetal lung adenocarcinoma is even rarer, requiring more research to find the best treatment strategies.