# Risk Factors & Symptoms

Who gets lung cancer, what causes it in people who never smoked, why most cases are found
late, what symptoms to watch for, and who qualifies for screening.

## 1 — Who gets lung cancer?

Tobacco is the leading cause — but **anyone can be affected**, including people who have
never smoked.

Attributable share of lung cancer cases by risk factor:

| Risk factor | Share |
|---|---|
| Tobacco and smoking | 85% |
| Radon gas | 12% |
| Secondhand smoke | 7% |
| Occupational exposure | 5% |
| Other / genetics | 3% |

*Source: American Cancer Society, Cancer Facts & Figures 2024; CDC, NCHS.*

## 2 — The smoker's risk

Smokers are up to **25 times more likely** to develop lung cancer. Risk scales with how much
and how long a person smokes — measured in **pack-years**.

The good news: quitting at any age reduces risk. After 10–15 years, risk drops by roughly
half.

> **What is a pack-year?** Packs per day × years smoked. One pack a day for 20 years = 20
> pack-years.

*Source: NCI, SEER; U.S. Surgeon General's Report on Smoking & Health 2020.*

## 3 — Not just smokers

**One in five lung cancers** occurs in someone who has never smoked a cigarette. In
never-smokers, the most common causes are:

- **Radon gas** — the leading cause in never-smokers.
- **Secondhand smoke.**
- **Occupational exposure.**
- **Genetic mutations.**

> Radon test kits are available at most hardware stores for under $20. The EPA recommends
> testing every home.

*Source: CDC, Lung Cancer Among People Who Never Smoked, 2022; WHO IARC Monographs; EPA
Radon Guide 2023.*

## 4 — Found by accident

Most lung cancers produce **no symptoms** until they are already advanced. Stage at the time
of diagnosis, across all lung cancers:

| Stage | Extent | Share of diagnoses |
|---|---|---|
| Stage I | Localized | 16% |
| Stage II | Regional | 8% |
| Stage III | Extensive | 24% |
| Stage IV | Distant | 52% |

> Five-year survival at Stage I is 61%. At Stage IV it falls to just 6%. The earlier the
> catch, the better the odds.

*Source: NCI SEER Cancer Statistics 2023; NLST, NEJM 2011; ACS 2024.*

## 5 — B.R.E.A.T.H.E. — the symptom mnemonic

| Letter | Symptom | What it looks like |
|---|---|---|
| **B** | Breathlessness | Shortness of breath, even with mild activity. |
| **R** | Recurring infections | Pneumonia or bronchitis that keeps coming back. |
| **E** | Endless cough | A cough lasting more than 3 weeks, or a change in a chronic cough. |
| **A** | Aching chest | Chest, shoulder, or back pain that worsens with breathing. |
| **T** | Tiredness & weight loss | Unexplained fatigue or weight loss without trying. |
| **H** | Hemoptysis | Coughing up blood or blood-streaked mucus. |
| **E** | Enlarging lymph nodes | Swelling in the neck or above the collarbone. |

These symptoms do not always mean cancer — but any that persist for **more than 3 weeks**
deserve a conversation with a doctor.

*Source: ACS; NCCN NSCLC Guidelines 2024; NHS — Lung Cancer Symptoms.*

## 6 — When to get screened?

Annual low-dose CT can find lung cancer **before symptoms appear**. USPSTF 2021 LDCT
screening eligibility requires all three:

1. **Age** — 50 to 80 years.
2. **Smoking history** — 20 or more pack-years.
3. **Smoking status** — currently smoking, or quit within the last 15 years.

If you meet all three, talk to your doctor. Screening is covered by Medicare and most
insurers.

*Source: USPSTF 2021 Recommendation Statement; NLST, NEJM 2011; CMS Medicare Coverage.*

## Related

- [Lung Cancer Facts](https://nodule.app/lung-cancer-facts) — incidence, mortality, and
  survival context.
- [Risk calculator](https://nodule.app/calculator) — how smoking status feeds a validated
  nodule malignancy model.

---

*Educational use only · Not a medical device.* This document mirrors the page at
<https://nodule.app/risk-factors>.