Small-sized Pulmonary Adenocarcinoma Manifesting Skip-like Transition from Nonsolid Nodule: A Case Report

This report shows a case with a rare small-sized lung adenocarcinoma that rapidly progressed from a nonsolid nodule (NSN) to a solid nodule (SON) over a period of just 1 year after a very long-term observation from its first detection. In 2007, the patient was an asymptomatic 52-year-old man at the time of the first detection via chest low-dose computed tomography (CT) screening as part of a periodic medical checkup at our hospital. It revealed an abnormal shadow in another location of the lung field, necessitating a more thorough examination. Then, he visited our outpatient clinic for the first time and a workup examination was performed using thin-section CT (TSCT) images, which incidentally detected a small NSN with a maximum diameter of 1.2 cm in the mid-zone of the left upper lung field. Since it did not disappear in the periodic subsequent workup examinations, the patient was informed of the suspicious early lung adenocarcinoma each time; however, the patient desired to continue watchful waiting. The radiographical properties of the NSN remained almost unchanged until 2019, but in 2020, the inside of the nodule showed a skip-like change to a SON. Finally, because of the unexpectedly fast transition, consent for lobectomy could be obtained. Surgery was then performed, 13 years after its first detection, at an age of 65 years. The pathological findings revealed a 1.2 cm, pT1bN0M0, pStage IA2-adenocarcinoma, which was 90% of the acinar subtype with positive vascular permeation. Management of a NSN, that does not resolve and/or change, must continue watchful waiting, and at the very least continue follow-up with TSCT observation to ensure the safe and appropriate timing of excision using imaging as a marker of transition.