A substantial revision of the staging system was presented at the World Conference on Lung Cancer in Korea this week. This project involved multiple lung cancer experts from all over the world and from a variety of specialties over the last several years, who reviewed the data on approximately 100,000 lung cancer cases, both NSCLC and SCLC. They looked at various ways to break down this large database of cases in order to provide a more accurate prognosis for patients. In fact, while we use staging systems to guide our treatments, they are developed primarily as a way to predict the survival of patients by key variables. This new version, which will officially come into effect in 2009 but is being introduced now for the world to become familiar with and to have endorsed by other official cancer groups like the American Joint Committee on Cancer and the International Union Against Cancer.
First, just a few words on the concept of staging. The current cancer staging systems are classified by T N M, which stands for Tumor, Nodes, and Metastases. These are numbered from 0 to some other number. For lung cancer, tumor staging is up to 4, N is up to 3, and M is just up to 1 (you have metastatic disease or you don't). Various combinations lead to a final stage, and some factors trump others. For instance, you can have any T stage, even just a tiny tumor, but if you have N3 nodal stage (lymph nodes on the other side of the mid-chest from the main, or primary, tumor) and no metastases, the overall stage is IIIB. If you have a metastatic spot (M1), you have stage IV disease, no matter what the T stage or N stage. This page has a summary.
There is a lot to the new staging system, but here are some of the highlights:
T1 cancers, which are up to 3 cm in diameter, are to be divided into T1a and T1b at a breakpoint of 2 cm, reflecting that these smaller tumors have a particularly favorable prognosis.
T2 tumors, which were basically those beyond 3 cm and don't involve significant other structures in the chest, will now be split into those 3-5 cm and those 5-7 cm. And now those more than 7 cm are now classified as T3. This obviously reflects that larger tumors have a worse prognosis.
One of the most troubling aspects of the current systemhas been the T4 designation for a "satellite lesion" in the same lung lobe as the primary tumor, which is classified as stage IIIB. This is now being changed to T3 designation, reflecting the better prognosis of this situation than what would generally be expected for stage IIIB.
Other nodule(s) in the same lung but not the same lobe are now T4 instead of M1, also reflecting the significantly more favorable prognosis of patients with same lung nodules vs. more distant cancer spread.
Pleural involvement by either pleural nodules or a malignant pleural effusion (fluid outside of the lung with cancer cells in it) are now classified officially as M1 (metastatic). This change reflects the fact that malignant pleural effusions, now classified as T4 and IIIB overall, is actually treated the same as advanced/metastatic disease. No longer will we need to awkwardly say metastatic and "wet IIIB" to describe the advanced NSCLC population.
There were no substantial changes in N (nodal status) designation.
In the M staging system, what is now 0 or 1 (you have it or you don't) will now be divided into M1a and M1b. M1a is confined to nodules in the other side of the chest (same side being T4), and M1b is more distant spread.
The new staging system will break down the different TNM combinations as shown here:
Of note, the staging system doesn't automatically translate to changes in how we treat patients, but there will be refinements in our approaches, since this staging system also reflects on how we should be thinking about lung cancer.
Finally, I haven't specifically spoken on SCLC, but the key is that the TNM system, which hasn't really been used because oncologists use the "limited" vs. "extensive" staging classification that has the key implications for treatment plans. We'll see if the oncology world adopts the TNM system for SCLC, but it does suggest that there are distinctions in prognosis beyond just limited and extensive.
There will be much more to cover on the very large staging project, but that's the quick and dirty update.
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