Getting tissue: the biopsy
Images can suggest cancer, but only a tissue sample can prove it and name its exact type. There are several ways to reach a tumour. A bronchoscopy passes a thin camera down the airways, and from there a transbronchial biopsy can pinch tissue from a tumour near a bronchus. For nodules deeper in the lung, a needle can be passed through the chest wall under CT guidance. Each route trades reach against safety, and the choice depends on where the tumour sits.
A clever modern tool is endobronchial ultrasound (EBUS): a bronchoscope with an ultrasound probe on its tip can “see” lymph nodes through the airway wall and guide a needle into them. This lets doctors sample the central chest lymph nodes without surgery — which, as we will see, is the key to accurate staging.
How far has it spread? TNM staging
Once cancer is confirmed, staging answers the second great question: how far has it gone? Lung cancer uses the TNM system, which scores three things separately. T describes the primary tumour — its size and whether it has grown into nearby structures. N describes the lymph nodes — none, only nearby ones, or distant chest nodes involved. M describes metastasis — whether the cancer has spread to distant organs at all.
TNM combines into an overall stage (NSCLC, simplified): T = tumour size / local invasion (T1 small ... T4 large/invasive) N = lymph node spread (N0 none ... N3 far/opposite side) M = distant metastasis (M0 none, M1 present) Stage I small tumour, no nodes, no spread -> often surgery, aim to cure Stage II larger / nearby nodes -> surgery + extra treatment Stage III spread to central chest nodes -> combined treatments Stage IV distant metastasis (M1) -> systemic drug therapy Lower stage = more treatment options and better outlook.
Getting the N right is so important that it has its own name: mediastinal staging, the careful sampling of the lymph nodes in the centre of the chest, often by EBUS. Whether those central nodes contain cancer can be the difference between an operable, potentially curable tumour and one better treated with drugs and radiation. A PET-CT of the whole body and often a brain scan complete the picture by hunting for hidden distant spread.
Reading the tumour's molecular fingerprint
For advanced non-small-cell lung cancer — especially adenocarcinoma — the biopsy is now tested for specific genetic changes that drive the cancer's growth. The best known is the EGFR mutation, a fault in a growth-signal switch that is more common in never-smokers and in some Asian populations. Other markers (in genes such as ALK and ROS1) tell a similar story. Each marker, when present, can be matched to a drug aimed precisely at it.