Lung Cancer Subtypes & Lung-RADS
- Lung cancer splits into two big buckets: non-small cell (the common majority, ~85%) and small cell (fewer, faster, nastier).
- Adenocarcinoma loves the lung periphery and often shows up as a ground-glass or part-solid nodule; squamous cell tends to grow centrally and can cavitate.
- Small cell almost always presents as a bulky central mass with huge nodes — surgery is usually off the table by the time we see it.
- Lung-RADS is the report card for screening low-dose CT only: it scores nodules 0–4 and tells everyone the next move. It is not a staging system.
- Lung-RADS and the Fleischner criteria are different tools for different patients — don't mix them up.
"Lung cancer" sounds like one disease the way "dog" sounds like one animal. Then you meet a Chihuahua and a Great Dane and realize the word was hiding a lot. The subtypes behave so differently — where they grow, how fast, how we treat them — that lumping them together would be like writing one walking schedule for both dogs. So let's sort the pack, then talk about the scoring system that decides who gets called back from a screening scan.
The two big buckets
Pathologists divide lung cancer into non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC). That division isn't bureaucratic — it changes the entire game plan. NSCLC is the big tent, roughly 85% of cases, and at least in early stages it can be cut out. SCLC is the smaller, meaner cousin: it grows fast, spreads early, and we almost never reach for a scalpel.
NSCLC vs. SCLC is the first fork in the road because it decides whether surgery is even on the menu. Everything downstream — chemo, radiation, immunotherapy — flows from which bucket you're in.
Meet the NSCLC subtypes
Within the big tent, three subtypes do most of the work, and each has a personality.
| Subtype | Where it likes to live | Imaging tell |
|---|---|---|
| Adenocarcinoma | Lung periphery | Ground-glass or part-solid nodule; the most common type, including in never-smokers |
| Squamous cell carcinoma | Central airways | Tends to cavitate; can cause obstruction and post-obstructive collapse |
| Large cell carcinoma | Often peripheral | A "none of the above" bulky mass — a diagnosis of exclusion |
Adenocarcinoma is the suburb-dweller: it sets up out in the periphery of the lung. Early on it can be a faint, hazy ground-glass spot — the radiology equivalent of a smudge on a foggy windshield. As it gets more aggressive a solid component appears inside the haze, turning it into a part-solid nodule. That growing solid core is the part we worry about most.
Squamous cell carcinoma is the downtown type: central, near the big airways. Because it sits in the bronchi, it can block one and collapse the lung downstream, and it has a notable habit of cavitating — hollowing out a thick-walled hole in the middle, like a tumor that ate its own center.
The fast one: small cell
If NSCLC is a slow-burn problem, SCLC is the kitchen fire. It typically shows up as a bulky central mass with massive mediastinal and hilar lymphadenopathy — so much nodal disease that the original tumor can be hard to pick out of the bulk. It's strongly tied to smoking, and by the time it's visible it has usually already spread. That's why SCLC is staged and treated more by how far it's spread than by the neat anatomic carving-up we use for NSCLC.
A central mass swallowed by bulky nodes in a heavy smoker should make you think small cell early. The "is this resectable?" conversation is often over before it starts.
For the deeper dive on how we measure spread for any of these — tumor size, nodes, metastases — see Lung Cancer & Staging.
Lung-RADS: the screening report card
Now switch gears completely. Lung-RADS (the Lung Imaging Reporting and Data System) is the ACR's standardized scoring system for low-dose CT lung cancer screening — the scans done on high-risk people who feel completely fine. Think of it as the rubric a teacher uses so every paper gets graded the same way, no matter who's holding the red pen.
It sorts each screen into categories, and each category comes with a built-in recommendation:
| Category | Rough meaning | Typical next step |
|---|---|---|
| 0 | Incomplete — can't fully assess | Get prior scans or repeat imaging |
| 1 | Negative | Back to annual screening |
| 2 | Benign appearance/behavior | Continue annual screening |
| 3 | Probably benign | Shorter-interval follow-up CT |
| 4 (A/B/X) | Suspicious | Closer workup — more CT, PET/CT, and/or tissue sampling |
The key idea: higher number, more worried. A category 4 doesn't mean "cancer," it means "this earned a real look." The system folds in nodule size, whether it's solid, part-solid, or ground-glass, and crucially whether it grew since the last scan — because growth is one of the loudest alarm bells in nodule-land.
Lung-RADS is for screening CT only. An incidental nodule found on a CT ordered for some other reason is managed by the Fleischner Society recommendations, not Lung-RADS. Reaching for the wrong rubric gives the wrong follow-up interval. When in doubt, ask: "Was this a screening scan?"
How it all fits together
A nodule shows up — maybe on screening, maybe by accident. We describe it, measure it, and watch whether it changes, leaning on the broader logic of the solitary pulmonary nodule workup and staying alert to the everyday mimics of lung nodules that aren't cancer at all. If it does turn out to be cancer, the subtype tells us its personality and the staging tells us how far it's gone.
Subtypes describe what kind of lung cancer it is; Lung-RADS scores how suspicious a screening nodule looks. Keep those two jobs in separate drawers and the whole topic gets a lot less tangled.