Lung cancer refers to tumors originating in the lung parenchyma or within the bronchi.¹ Non-small-cell lung cancer (NSCLC) is the most common type of lung cancer, making up approximately 85% of lung cancers, and is defined as any type of epithelial lung cancer other than small cell lung cancer (SCLC).^2,3

NSCLC can be further subdivided on the basis of histological features into several categories, the most common of which are adenocarcinoma, squamous cell carcinoma, and large cell carcinoma.⁴ Large cell carcinoma has been defined in the past as a tumor that lacks morphologic evidence of either glandular or squamous differentiation.⁵ Figure 1 shows some of the more common histological subtypes of tumors found in NSCLC.³

However, increasing evidence shows that a large proportion of these tumors can be subtyped further using modern immunohistochemical and molecular methods.⁵ These molecular subtypes are discussed in more detail in the section “Molecular subtypes of NSCLC”.

In high-risk groups, such as those with tobacco exposure, one of the screening methods shown to reduce mortality is low-dose computed tomography (CT).^7,8 Lung cancer may present with symptoms, such as cough or chest pain, or be found on chest imaging, with additional investigations aiming to confirm the diagnosis and determine the extent of the disease.⁹ Factors such as stage, histology, presence and type of mutation, and the presence of comorbidities will define the prognosis and treatment options available to a patient.^10–13

Determination of stage has important prognostic and treatment implications.¹⁰ Procedures used to establish stage include a physical examination and radiological assessment.^14,15 The disease is staged according to the 8th edition of the American Joint Committee on Cancer (AJCC) TNM system, which is based on:¹⁶

• Size and extent of main tumor (T)
• Spread to nearby lymph nodes (N)
• Metastasis (M) to distant sites