SC24.01 Risk Assessment in the Management of Pulmonary Nodules

Abstract

Solitary pulmonary nodules are seen on approximately 0.1% of all chest X-ray films.1 High-resolution computed tomography (HRCT), which is used in lung cancer screening programs, can detect pulmonary nodules that are smaller than those detected by conventional radiography. The radiological diagnosis and treatment of these small pulmonary nodules are now the focus of lung cancer research. The timely detection of lung cancers is essential for successful treatment. The guidelines and recommendations for the management of pulmonary nodules include follow up, nonsurgical biopsy, or surgery; and are based on the size of the nodule, and ground glass opacity (GGO) ratio or size of the solid component.2-4 The diagnosis of a pulmonary nodule is frequently problematic. The management of pulmonary nodules is based on their characteristics. When a pulmonary nodule is monitored by CT, the important features include not only its size but also its density. According to the guidelines of the American College of Chest Physicians, solid nodules measuring > 8 mm in diameter need further examination.3 The Fleischner Society for Thoracic Imaging and Diagnosis uses a cutoff diameter of 5 mm for decision making for subsolid nodules.2 It should be kept in mind that solid nodules that are suspicious for lung cancer are frequently invasive. A subsolid nodule can be classified as a pure ground glass nodule (GGN) or part-solid nodule. Subsolid nodules grow slowly and may develop a solid component. The HRCT findings of early lung adenocarcinomas were significantly correlated with the histopathologic findings of the resected specimens.5 In the evaluation of subsolid nodules, the features indicating noninvasive lung adenocarcinoma include tumor disappearance rate, diameter of consolidation, and GGO ratio.6 However, even HRCT cannot accurately assess the areas of solid opacities or GGO, and results might vary between investigators. In the upcoming 8th TNM classification, the Lung Cancer Staging Project of the International Association for the Study of Lung Cancer showed that the solid part of a nodule on HRCT represents the clinical T factor, and that measurement of the solid part is essential for lung cancer staging.5 Positron emission tomography (PET)-CT has a clearly established role in lung cancer clinical practice. Based on the pretest probability, PET-CT should be used for patients with a solid, indeterminate nodule > 8 mm in size.3,4 For adenocarcinomas in situ (AIS) and minimally invasive adenocarcinomas (MIA) of the lung that show solid opacities on HRCT, the preoperative PET-CT and thin-section CT findings together can provide information on the aggressiveness of the tumor. Our study group found that these modalities used together could detect aggressive lung cancers in clinical stage IA (Fig. 1).7 However, since PET-CT can show false-negative results for slow-growing and low-grade lung malignancies, we think that HRCT is the best modality for identifying indolent lung cancers. Transthoracic biopsy, bronchoscopy, or surgery is used for obtaining specimens for histopathological diagnosis. The definitive diagnosis of small pulmonary nodules, especially GGO-dominant nodules, is challenging. The diagnostic yields of percutaneous CT-guided fine needle aspiration biopsy for GGO-dominant and solid-dominant lesions were 51.2% and 75.6%, respectively (p = 0.018).9 The diagnostic yield of GGO-dominant lesions < 10 mm was 35.2%. Since invasive biopsy is not without risk, a histopathological diagnosis should be limited to nonsurgical candidates. For cases with high likelihood of lung cancer, a surgical biopsy followed by lung resection might be warranted. Although surgery might be performed on patients with benign nodules, it does provide the definitive diagnosis. If surgery is performed after careful preoperative assessment, the surgical mortality is very low, and the surgical risk may be acceptable. While lobectomy is the standard procedure for lung cancers, sublobar resection, meaning segmentectomy or wedge resection, might be justified for patients with noninvasive small lung cancers. However, to date, which procedure, sublobar resection or lobectomy, provides a better outcome remains unclear in these cases, since prospective randomized control trials are ongoing (JCOG0802/WJOG4607L8 and CALGB140503). One of the concerns in sublobar resection is recurrence at the surgical margin (Fig. 2). Recurrence at the surgical margin might be accounted for by tumor cells spreading via air spaces.10 Accurate intraoperative cytology and adequate surgical margins have been reported to be important for preventing recurrence at the surgical margin. Another concern is lymph node metastasis. In a prospective radiological study for clinical stage IA lung cancer, 47 of 545 (8.6%) patients had lymph node metastasis.6 Sublobar resection, especially wedge resection, does not allow evaluation of lymph nodes for metastatic disease. HRCT findings play an important role in discriminating the biological behaviors of pulmonary nodules. The definitive diagnosis by HRCT can be difficult, and the combination of HRCT and PET-CT might be beneficial. Randomized control trials should clarify the role of sublobar resection in treating patients with noninvasive lung cancer.Figure 2View Large Image Figure ViewerDownload Hi-res image Download (PPT)