The new, 7th Edition of the TNM (tumor, nodes, metastases) staging system for lung cancer came into use earlier this year and has led to changes in the staging of about 15% of lung cancers compared with what they'd have been staged as under the 6th edition.

The staging of lung cancer makes the distinction of whether there are any lymph nodes involved with cancer, and if so, whether they are within the lung that houses the primary cancer or outside of it; if the latter, a distinction is made among mid-chest nodes on the same side as the main tumor (N2), mid-chest nodes on the opposite side from the main tumor (N3), or above the collarbone (N3).