# Glossary — Terminology Library Plain-language definitions of common terms used in lung cancer screening and pulmonary nodule imaging. All entries are grounded in published clinical guidelines — Lung-RADS 2022, the Fleischner Society 2017 guidelines, NCCN Guidelines v2024, and current oncology literature. This document is generated directly from the same data that renders the page, so the two cannot disagree. ## Pulmonary Nodules ### Ground Glass Opacity (GGO) A hazy area of increased lung density on CT that does not obscure the underlying bronchial structures or pulmonary vessels. Appears as a faint "frosted glass" haze. **Why it matters:** Ground glass nodules tend to grow more slowly than solid nodules and may represent early adenocarcinoma or non-malignant processes. They often require longer-term surveillance. *Source: Fleischner Society Guidelines, Radiology 2017* ### Lobulation An irregular, bumpy, or scalloped nodule border, caused by differential growth rates within the nodule. **Why it matters:** Lobulated margins carry intermediate suspicion between smooth and spiculated margins. They may indicate uneven tumor growth. *Source: Lung-RADS v2022, American College of Radiology* ### Part-Solid Nodule A nodule that contains both ground glass and solid components. The solid component does not allow visualization of underlying lung architecture. **Why it matters:** Part-solid nodules with a solid component ≥6 mm carry a higher risk of malignancy than pure ground glass or solid nodules of similar size. They require close surveillance. *Source: Fleischner Society Guidelines, Radiology 2017; Lung-RADS v2022* ### Pulmonary Nodule A small, round or oval growth in the lung, typically less than 30 mm in diameter. Nodules larger than 30 mm are generally classified as masses. **Why it matters:** Pulmonary nodules are one of the most common incidental findings on chest CT scans. Their size, density, and margin characteristics guide follow-up recommendations. *Source: Fleischner Society Guidelines, Radiology 2017* ### Spiculation Linear strands radiating outward from a nodule margin, giving a "sunburst" or "corona radiata" appearance on CT. **Why it matters:** Spiculated margins are associated with higher suspicion for malignancy, as they often reflect tumor invasion into surrounding tissue. *Source: Lung-RADS v2022, American College of Radiology* ## Screening & Guidelines ### Fleischner Society Guidelines Evidence-based recommendations for the management of incidentally detected pulmonary nodules — nodules found on CT performed for reasons other than lung cancer screening. **Why it matters:** The Fleischner guidelines differ from Lung-RADS: they apply to incidental nodule findings in patients ≥35 years old, not screening-detected nodules. Knowing which framework applies to a given nodule is important for appropriate follow-up. *Source: MacMahon et al., Radiology 2017* ### Low-Dose CT (LDCT) A computed tomography scan of the chest performed at a lower radiation dose than standard CT, used specifically for lung cancer screening. **Why it matters:** LDCT is the only screening modality shown to reduce lung cancer mortality in high-risk individuals. It detects nodules too small to cause symptoms. *Source: National Lung Screening Trial (NLST); USPSTF 2021* ### Lung-RADS Lung Imaging Reporting and Data System — a standardized reporting system developed by the American College of Radiology to categorize CT lung screening findings and guide follow-up. **Why it matters:** Lung-RADS provides radiologists with a consistent framework to communicate nodule findings and recommend follow-up intervals, reducing variability in interpretation. *Source: American College of Radiology, Lung-RADS v2022* ### Pack-Years A measure of cumulative tobacco exposure: packs smoked per day × years smoked. For example, 1 pack/day for 20 years = 20 pack-years. **Why it matters:** Pack-year history is a key criterion for lung cancer screening eligibility under USPSTF guidelines and Lung-RADS. A ≥20 pack-year history in eligible individuals is a threshold for LDCT screening. *Source: USPSTF 2021; Lung-RADS v2022* ## Lung Cancer ### NSCLC (Non-Small Cell Lung Cancer) The most common type of lung cancer, accounting for ~85% of all cases. NSCLC includes adenocarcinoma, squamous cell carcinoma, and large cell carcinoma subtypes. **Why it matters:** Most biomarker testing guidelines and driver mutation research apply specifically to NSCLC — particularly the adenocarcinoma subtype. Knowing whether a lung cancer is NSCLC or small cell (SCLC) determines which treatment pathways and testing protocols are applicable. *Source: NCI; NCCN Guidelines v2024* ## Biomarkers & Testing ### Biomarker A measurable biological characteristic — a protein, gene, or other molecule — that provides information about a disease process or treatment response. **Why it matters:** In lung cancer, biomarkers guide treatment decisions by identifying specific molecular targets. A biomarker can distinguish patients who will respond to a targeted therapy from those who won't. *Source: FDA Biomarker Working Group, 2016; NCI Dictionary of Cancer Terms* ### Driver Mutation A genetic change in a tumor cell that actively drives the cancer to grow and spread by locking a growth signal in the "on" position. Unlike passenger mutations, driver mutations are responsible for the tumor's progression. **Why it matters:** Driver mutations are the molecular targets of targeted therapy. Because they're required for tumor growth, drugs that block them can dramatically slow or stop the cancer — often with fewer side effects than chemotherapy. *Source: NCCN Guidelines v2024; NCI* ### Liquid Biopsy A blood test that detects tumor DNA fragments (ctDNA or cell-free DNA) circulating in the bloodstream. It can identify driver mutations without requiring a tissue sample. **Why it matters:** Liquid biopsy offers a less invasive alternative when tumor tissue is inaccessible or insufficient. NCCN recommends it as a complementary or alternative approach for molecular profiling in advanced NSCLC. *Source: NCCN Guidelines v2024; ASCO Clinical Practice Update 2022* ### Next-Generation Sequencing (NGS) A high-throughput DNA sequencing technology that reads a tumor's genetic code and screens for hundreds of mutations simultaneously in a single test. Also called broad molecular profiling. **Why it matters:** NGS is the recommended method for comprehensive biomarker testing in advanced NSCLC. A single panel can identify all actionable driver mutations and PD-L1 status at once, avoiding the need for multiple sequential tests. *Source: NCCN Guidelines v2024* ## Key Mutations ### ALK (Anaplastic Lymphoma Kinase) A gene that, when rearranged or fused with another gene, produces an abnormal protein that drives cell growth. ALK rearrangements occur in ~5% of NSCLC, often in younger patients and never-smokers. **Why it matters:** ALK-positive NSCLC responds to ALK inhibitors such as alectinib, which penetrates the brain well — important because ALK+ cancers have a higher tendency to spread there. *Source: NCCN Guidelines v2024; ALEX Trial, NEJM 2017* ### EGFR (Epidermal Growth Factor Receptor) A protein that normally regulates cell growth. In ~15% of non-small cell lung cancers, a mutation in the EGFR gene locks this receptor in the "on" position, driving continuous cell division. **Why it matters:** EGFR-mutated NSCLC responds to EGFR inhibitors such as osimertinib, which can achieve response rates above 75% — compared to ~30% with standard chemotherapy. *Source: NCCN Guidelines v2024; FLAURA Trial, NEJM 2018* ### KRAS G12C A specific point mutation in the KRAS gene where glycine is substituted with cysteine at position 12. KRAS mutations drive ~13% of NSCLC and are more common in current or former smokers. **Why it matters:** KRAS was the first oncogene ever discovered (1982) but was considered undruggable for nearly 40 years. Sotorasib, FDA-approved in 2021, was the first drug to successfully target KRAS G12C — a landmark breakthrough in oncology. *Source: NCCN Guidelines v2024; CodeBreak 100 Trial, NEJM 2021* ### ROS1 A gene involved in cell growth signaling. ROS1 rearrangements — where ROS1 fuses with another gene — occur in ~2% of NSCLC and structurally resemble ALK rearrangements. **Why it matters:** ROS1-rearranged NSCLC responds to ROS1 inhibitors, including crizotinib, which was originally developed for ALK. NCCN recommends ROS1 testing at diagnosis for all patients with advanced NSCLC. *Source: NCCN Guidelines v2024; Shaw et al., NEJM 2014* ## Treatment ### Checkpoint Inhibitor A class of immunotherapy drugs that block proteins (such as PD-1 or PD-L1) that cancer cells use to evade immune detection. By removing this "checkpoint," the drugs allow the immune system to recognize and attack the tumor. **Why it matters:** Checkpoint inhibitors such as pembrolizumab are a standard treatment for NSCLC patients with high PD-L1 expression and no actionable driver mutations. They work through a fundamentally different mechanism than targeted therapy. *Source: NCI; FDA; KEYNOTE-024 Trial, NEJM 2016* ### PD-L1 (Programmed Death-Ligand 1) A protein expressed on some tumor cells that binds to immune checkpoints, effectively hiding the tumor from the immune system. High PD-L1 expression is a predictive biomarker for immunotherapy response. **Why it matters:** PD-L1 status is tested alongside driver mutations at diagnosis for all advanced NSCLC patients. High expression identifies patients likely to benefit from checkpoint inhibitor immunotherapy, independent of driver mutation status. *Source: NCCN Guidelines v2024; FDA labeling (pembrolizumab)* ### Targeted Therapy Cancer treatment designed to block specific molecules or pathways that cancer cells depend on to grow and survive. In lung cancer, targeted therapies are matched to specific driver mutations identified through biomarker testing. **Why it matters:** Targeted therapies are more precise than chemotherapy and achieve significantly higher response rates when matched to the correct driver mutation — representing a major advance in personalized cancer care. *Source: NCI; NCCN Guidelines v2024* ## Related - [Nodule Types](https://nodule.app/tutorial) — the concepts these terms describe. - [References and disclaimer](https://nodule.app/references) — full citations for every guideline. --- *Educational use only · Not a medical device.* This document mirrors the page at .