Atypical Spread With Lung Shrinkage and Cystic Changes in Bilateral Lepidic Adenocarcinoma

Lepidic adenocarcinoma is a subtype of lung cancer that grows along the alveolar walls and frequently harbours epidermal growth factor receptor (EGFR) mutations. We report a unique case of symmetrical lepidic adenocarcinoma that progressed to cystic changes and demonstrated a distinct discrepancy between the radiological and physiological findings during EGFR-tyrosine kinase inhibitors (TKI) treatment. A 44-year-old man presented with a right upper lobe mass and bilateral, symmetrical ground-glass nodules (GGNs), both harbouring EGFR L858R mutations. Chemotherapy, including osimertinib, induced a stepwise transition from the initial GGN attenuation to extensive bilateral cystic degeneration accompanied by restrictive pulmonary dysfunction, which is attributed to the rapid tumour regression and subsequent architectural remodelling. This case underscores the importance of recognizing unique treatment-related changes in the setting of diffuse lepidic tumour involvement. Clinicians should be aware of these atypical imaging manifestations in patients with extensive lepidic adenocarcinoma receiving potent EGFR-TKIs.