The most pivotal study supporting the value of screening for lung cancer is the National Lung cancer Screening Trial (NLST), which revealed a 20% improvement in overall survival in patients with sufficiently high risk of lung cancer and who underwent an annual chest CT scans vs. chest x-ray over a three year period. This significant benefit was seen in patients who were sufficiently high risk for lung cancer -- patients age 55-75 and with at least a 30 "pack-year" smoking history (the product of number of years smoking x average number of packs smoked per day).
But even after this survival benefit was seen,there has been plenty of controversy that followed. Screening chest CT scans detects not only some true, life threatening lung cancer but also many, many benign lung nodules in people who undergo these scans. News of such nodules often cause people cause tremendous anxiety, along with a need for additional imaging and often invasive procedures to clarify whether the detected nodules are more likely to represent a benign finding or a real cancer.
Some patients and many institutions favor extending the screening of high risk patients to those at significantly lower risk, such as those who are younger, have minimal smoking history, perhaps even a never-smoker with a family history. But there is a real danger that if screening is applied people at low risk of actually having lung cancer, it's far more likely that any nodules detected will be benign but will still lead to all of the anxiety, extra scans, and sometimes invasive procedures... just not to lives saved from lung cancer.
Why do screening on people who are at lower risk? Many people are nervous about lung cancer, and some institutions that make money by doing scans and procedures may be more than happy to oblige them or even feed their fears. We need to be judicious about how to use CT screening for lung cancer in a way that can save the most lives but lead to a minimal amount of extra scans, unneeded biopsies, and profound anxiety.
What is remarkably instructive as we struggle with these issues is a a new analysis of the results from the NLST study that stratified eligible patients by level of risk, which demonstrates the real risks of lung cancer vs. "false positives" -- cases where the nodules required action and probably caused anxiety, but it wasn't cancer. The investigators looked at a wide range of relevant variables for risk of lung cancer (age, sex, years since quitting, pack-years of tobacco exposure, family history, etc.), then divided the participants into 5 quintiles (5 equally sized groups). As we would expect, major differences were noted in the efficacy and significance of an abnormal result depending on whether people eligible for the NLST were higher or lower on the risk spectrum.
For those in the highest risk quintile, screening detected 65 false positives for every life saved from lung cancer, and you needed to screen 161 people with this level of risk to save a life. That's plenty of people going through a lot of anxiety and extra scans, but that's a relatively good result for a cancer screening study. Unfortunately, the results were much less impressive for the lowest risk range of patients eligible for the screening study; in this group, screening detected 1648 false positives for every lung cancer death prevented. You needed to screen over 5000 people with this level of risk to save a single person from a lung cancer death.
It's possible that you could say that we should screen EVERYONE for lung cancer or at least extend to a broad range, but these findings underscore that the lower a person's risk of actually having what you're screening for, the more likely it is that what you find is not what you're really looking for. You end up doing thousands and thousands of scans, requiring thousands of additional scans and many biopsies, only to actually help a tiny minority of people. And this needs to be weighed against the extreme anxiety and even potential risk from all of the unhelpful scans and invasive procedures to prove that someone with a very low risk actually has nothing serious happening. Our discussion forums are filled with people paralyzed by fear that they have cancer but who have nothing more than a benign nodule. They often express profound regret for undergoing these scans.
Of course, I remain a proponent of lung cancer screening, but only in higher risk people. The 20% improvement in survival from lung cancer is actually much higher in the highest risk patients on that trial, and it's far lower in the lower risk people who participated. Screening is a double-edged sword.
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