• lung cancer
• non-small cell lung cancer

Due to the prevalence of low-dose computed tomography (LDCT) screening, the detection rate of lung cancer presenting as multiple ground-glass opacities (GGOs) is increasing. In statements from the Fleischner Society and the International Association for the Study of Lung Cancer (IASLC) Staging and Prognostic Factors Committee, GGOs are considered as multiple primary lung cancers and at the early stage of tumorigenesis.1 2 Accumulating evidence supports the notion that metastasis in human cancer can occur at an early stage of disease progression. Whether multiple GGOs may represent intrapulmonary metastases remains unclear. In two patients with multiple GGOs, we found that two of the multiple GGOs in each patient shared somatic mutations based on exome sequencing, indicative of intrapulmonary metastasis. This finding, for the first time to our knowledge, shows that metastasis can occur among GGOs, even pure GGOs.

The two patients (P1 and P2) were both non-smokers. Detailed clinicopathological characteristics are summarised in (figure 1A). P1 was a 62-year-old woman who presented with nine GGOs including two in the right middle lobe (RML), three in the right lower lobe (RLL), three in the left upper lobe (LUL) and one in the left lower lobe (LLL) (figure 1B). She underwent RLL lobectomy and RML wedge resection in January 2015. The five resected nodules were all diagnosed as lung adenocarcinomas. Four months later she underwent LUL and LLL wedge resections. Three of the four resected nodules were diagnosed as lung adenocarcinomas. All eight malignant lesions were pathological T1–T2 tumours without lymphovascular invasion (online supplementary figure 1). No lymph node metastasis was detected. P2 was a 44-year-old woman who presented with eight GGOs including six in the right upper lobe (RUL) and two in the LUL (figure 1C). Radiologically, all of the eight lesions were pure GGOs <15 mm (range 4–14 mm). She only underwent RUL lobectomy and six nodules were removed. All …