The current cancer staging system (TNM) was conceived to codify the anatomic extent of disease at diagnosis to provide an accurate prognostic factor for solid tumors-in a way that was simple, easy-to-use, and could be used worldwide. TNM assess cancer progression in patients based on three criteria: the local extent of the cancer within the site of origin (T), the degree of metastatic involvement of the regional lymph nodes (N), and the presence or absence of distant metastatic disease.
But, in the current era of precision medicine, experts say the system is too simple.
So, in 2014 the American Joint Committee on Cancer-the group that developed and maintains the cancer staging system-formed a committee of experts, the Precision Medicine Core (PMC), to develop new criteria to evaluate cancer risk calculators to enhance the current staging system and to determine which ones should be endorsed by the AJCC. Last month that committee published guidelines containing these new criteria, which they say will promote more accurate and individualized cancer predictions, guide more precise treatments, and improve patient survival rates and outcomes. The guidelines are published in a paper online ahead of print in CA: A Cancer Journal for Clinicians (DOI: 10.3322/caac.21339).
The next step will be the various cancer disease management teams of the AJCC reviewing the statistical prediction models that have been created and published in the literature in their respective areas-and making recommendations to the PMC. The PMC will make the final decisions on which models will be endorsed.
In an email interview, PMC member and lead author of the guidelines Michael Kattan, PhD, MBA, Chair of the Department of Quantitative Health Sciences at Cleveland Clinic's Lerner Research Institute, elaborated on why these guidelines are important and why the current staging system needs revamping.
1 What are the limitations of the current cancer staging system?
"It lumps patients within a stage with respect to their prognosis. All patients who are stage II would share the same prognosis-and that's not a very accurate approach. A 'bad II' might have a worse prognosis than a 'favorable III,' but the staging system won't allow this [variability]. A statistical prediction model won't lump patients like that into groups."
2 These new guidelines do not replace the current staging system, right? Could you explain how they will be used?
"Right. The guidelines will permit the addition of statistical prediction models to accompany [cancer] staging systems. The models do not replace or affect the staging systems.
"However, there may come a day when the staging system is no longer useful in the presence of a good statistical prediction model. It is not inconceivable to, at some point, have only statistical prediction models without staging systems because the models predict outcomes more accurately."
3 How are better statistical prediction models and cancer staging systems related to precision medicine?
"All of this essentially means predictions that are better tailored to the individual patient. We move away from considering all patients within a particular stage to be the same. Instead, we take everything we know about you and make the best prediction that we can.
"The next step is reviewing the literature to find existing statistical prediction models that meet requirements. Those [models] will be endorsed. Next we challenge researchers to build more that satisfy our requirements."
Access More "3 Questions On..."
Read more answers straight from the experts on the latest news and provocative topics in Sarah DiGiulio's award-winning blog: bit.ly/OT-3Questions