Persistent pulmonary subsolid nodules: How long should they be observed until clinically relevant growth occurs?

During the first two decades of 21^st century, there has been remarkable advance in the knowledge about lung cancer. One of the most important advances is persistent pulmonary subsolid nodules (SSNs) including pure ground-glass nodules (GGNs) and part-solid nodules (PSNs). Pulmonary SSNs, when persistent, have high probability of being pulmonary adenocarcinomas spectrum pathologically, and ironically show very indolent clinical courses over follow-ups (1-3). Many researchers investigated the natural history of persistent pulmonary SSNs, which included the frequency and pattern of interval growth, and the growth rate, to determine optimal management plan of patients with these nodules (4-8). However, uncertainty still remains on the natural course of persistent SSNs, especially with respect to the long-term consequences and ideal timing for surgical resection.