Some presentations of non-small cell lung cancer (NSCLC) are described by clinicians as having ground glass opacity (GGO), the hazy gray areas observed on CT scans that do not obscure the underlying vascular areas. GGO suggests an increased density within the lungs and has also been associated with infection, chronic interstitial disease, and acute alveolar disease. GGO has also been identified in recent studies as a potential prognostic tool.
Current Staging System
The Union for International Cancer Control (UICC) has developed a staging system that is the only established prognostic modality to address the risk of cancer reoccurrence based on tumor descriptors. Although this system is continually updated, it does not currently include GGO.
“Recent studies of patients with surgically resected stage I NSCLC have reported that the prognosis of patients who have tumors with a GGO component (part-solid tumors) is significantly better than patients with pure solid tumors (solid tumors), even if the solid component of both tumors has the same diameter,” write Akira Hamada, MD, and colleagues in JTO Clinical and Research Reports. “These results suggest that the presence of GGO component should be considered in the tumor [T] descriptor.”
Including GGO as a Descriptor
Dr. Hamada and colleagues developed a study that retrospectively analyzed data on 1,133 patients with NSCLC who underwent pulmonary resection. They then narrowed the group to 384 patients who underwent complete resection by lobectomy or pneumonectomy for clinical stage I NSCLC. This group was separated into two groups based on the description of their tumors as part-solid (ie, presence of GGO) or solid. The median follow-up of these 384 patients was 77 months.
Dr. Hamada and colleagues observed that although the current UICC Tumor-Node-Metastases (TNM) classification well separated recurrence-free survival (RFS) and overall survival (OS), it did not, however, predict patient outcomes in the part-solid and solid groups. Patients who were observed to have tumors with GGO reported a better prognosis compared with patients who had pure solid tumors—even within the same stage of cancer.
As such, Dr. Hamada and colleagues proposed a novel tumor descriptor classification, such that IA stood for part-solid tumors, ID for solid tumors leas or equal to 3 cm, and IC for solid tumors between 3 and 4 cm.
Although the aim of this study was to encourage a better TNM staging system that includes the GGO descriptor, the authors acknowledge that because the current system is rigid and includes clinical, surgical, and pathologic observations, determining how to include this across the structure will need to be determined in the future. Dr. Hamada and team wrote that “this novel clinical staging system predicted patient prognosis better than the current TNM classification. On pathologic evaluation, the partsolid group always had better prognoses than the solid group in each subgroup divided by pathologic grade.”