NSCLC is any type of epithelial lung cancer other than small cell lung cancer (SCLC). The most common types of NSCLC are squamous cell carcinoma, large cell carcinoma, and adenocarcinoma, but there are several other types that occur less frequently, and all types can occur in unusual histologic variants. Although NSCLCs are associated with cigarette smoke, adenocarcinomas may be found in patients who have never smoked. As a class, NSCLCs are relatively insensitive to chemotherapy and radiation therapy compared with SCLC. Patients with resectable disease may be cured by surgery or surgery followed by chemotherapy. Local control can be achieved with radiation therapy in a large number of patients with unresectable disease, but cure is seen only in a small number of patients. Patients with locally advanced unresectable disease may achieve long-term survival with radiation therapy combined with chemotherapy. Patients with advanced metastatic disease may achieve improved survival and palliation of symptoms with chemotherapy, targeted agents, and other supportive measures.
Incidence and Mortality
Estimated new cases and deaths from lung cancer (non-small cell and small cell combined) in the United States in 2011:
- New cases: 221,130.
- Deaths: 156,940.
Lung cancer is the leading cause of cancer-related mortality in the United States. The 5-year relative survival rate from 1995 to 2001 for patients with lung cancer was 15.7%. The 5-year relative survival rate varies markedly depending on the stage at diagnosis, from 49% to 16% to 2% for patients with local, regional, and distant stage disease, respectively.
NSCLC arises from the epithelial cells of the lung of the central bronchi to terminal alveoli. The histological type of NSCLC correlates with site of origin, reflecting the variation in respiratory tract epithelium of the bronchi to alveoli. Squamous cell carcinoma usually starts near a central bronchus. Adenocarcinoma and bronchioloalveolar carcinoma usually originate in peripheral lung tissue.
Anatomy of the respiratory system.
Smoking-related lung carcinogenesis is a multistep process. Squamous cell carcinoma and adenocarcinoma have defined premalignant precursor lesions. Before becoming invasive, lung epithelium may undergo morphological changes that include the following:
- Carcinoma in situ.
Dysplasia and carcinoma in situ are considered the principal premalignant lesions because they are more likely to progress to invasive cancer and less likely to spontaneously regress.
In addition, after resection of a lung cancer, there is a 1% to 2% risk per patient per year that a second lung cancer will occur.
NSCLC is a heterogeneous aggregate of histologies. The most common histologies include the following:
- Epidermoid or squamous cell carcinoma.
- Large cell carcinoma.
These histologies are often classified together because approaches to diagnosis, staging, prognosis, and treatment are similar.
Several risk factors contribute to the development of lung cancer. These risk factors may include the following:
- Cigarette, pipe, or cigar smoking.
- Exposure to second-hand smoke, radon, arsenic, asbestos, chromates, chloromethyl ethers, nickel, polycyclic aromatic hydrocarbons, radon progeny, other agents, and air pollution.
- Radiation therapy to the breast or chest.