Transition From Distinct Types of KRAS Mutation-Harboring Multifocal Lung Adenocarcinoma to Rhabdoid Tumor: A Longitudinal Follow-Up.

BACKGROUND Rhabdoid tumor (RT) of the lung is a rare and aggressive malignancy. The origin of and the mutation responsible for RT are entirely unknown. The distinction between RT associated with subtypes of lung cancer and SMARCA4-deficient thoracic sarcomas is also unknown. CASE REPORT Three pulmonary subsolid nodules in the right S6, left S6, and left S8 were identified in a 78-year-old Japanese woman. At 3 and 9 months later, a chest CT showed unchanged sizes, but at 15 months the development of a 37-mm mass in the right S6 was observed. The patient's systemic condition deteriorated rapidly, and she died 1 month later. An autopsy revealed that the mass consisted of 90% RT and 10% lung adenocarcinoma. There were another 2 adenocarcinoma lesions in the left lung. KRAS mutation analyses revealed the same KRAS mutation (G12D) in the adenocarcinoma and RT components in the identical mass and metastatic RT, indicating that all of these components had the same clonality. A different KRAS mutation in each of the 3 adenocarcinoma lesions was detected (right S6: G12D, left S6: A59G, left S8: G12C), indicating that the multiple adenocarcinoma lesions were truly multifocal lung adenocarcinoma. The adenocarcinoma and RT components retained SMARCA4 expression. CONCLUSIONS This is the first evidence of RT originating from multifocal lung adenocarcinoma. KRAS mutation is thought to be responsible for the RT's emergence via the epithelial-mesenchymal transition. Patients with multiple subsolid nodules should be followed closely; aggressive surgical intervention should be considered given concerns about the evolution of this aggressive malignancy.