Thursday, October 26, 2006

Thoracic imaging for lung cancer screening-here we go again

In the October 26,2006 issue of the New England Journal of Medicine we find a clinical study and an editorial about lung cancer screening using CT which should rekindle the decades old arguments about this topic. ( Survival of Patients with stage I Lung Cancer detected on CT Screening, NEJM 355;17, p. 1763). So high profile are NEJM articles with pickup and amplification by the news media that I will not be surprised when smokers and possibly folks who worked around asbestos and possibly other lung carcinogens will be asking their physicians for chest CTs. A brief review of the current study is found here.

A convincing advocate of the value of imaging screening for early lung cancer has been Dr. Gary M. Strauss. Some of his views can be found here. When we talk about screening we have to talk about the difference between survival rate and mortality rate.The latter is defined as the total number of deaths from the disease in question divided by total number tested. Survival rate is defined as numbers of survivors after some time period divided by total number diagnosed with cancer. If the screening technique were to detect significant numbers of indolent cancers then the survival rate might appear to be improved after the institution of the screening test while the mortality rate might be unchanged. Prostate cancer screening with periodic PSA measurements is sometimes accused of being an example of that. After spending a few decades in the pulmonary disease business I was not impressed with the large number of indolent or clinically insignificant lung cancers.Every pulmonary doctor remembers the occasional case of cured lung cancer that happened to fortunately be detected by a chest xray done for whatever reason. The coin lesions (less than 3 cm by definition) have a much higher cure rate than lung cancers as a whole. All of that leads to the intuitive appeal l (or maybe just hope) that if we could come up with a way to catch lung cancer early the current rather dismal survival rate of lung cancer would improve.

Conventional wisdom contains the nugget that in regard to screening one should use the cause specific mortality as a measure of efficacy not the survival over a given time period.. Strauss has taken the opposite view. More of his thoughts can be found here and here and here.

This brings us to the current study,I-ELCAP aka The International EarlyLung cancer Action Program. It is survival rates that are emphasized in this study (so the issue of lead time bias has to be raised) and the numbers seem impressive. The study is very large with over 31,000 asymptomatic persons at risk of lung cancer being screening with low dose spiral CT and then evaluated with a detailed protocol that utilized followup CTs, PET scans and skinny needle biopsy. They report a "estimated 10-year survival of 88% in the subgroup with clinical stage I lung cancer"

A great deal has happened since the early chest x-ray lung cancer screening projects. We have spiral CT, PET scans and skinny needle biopsies.Perhaps we can now detect lungs cancer early enough (that is small enough?) to remove them while they is still time. Before I reviewed the article I had assumed they were talking about non-small cell cancers (NSCLC) since the small cell variety seems to be another animal entirely. However, no mention is made on survival for each cell type or any indication that they were managed differently and there were 7 small cell cancers detected on the annual screening.Were they resected also? Is it possible that we can actually detect and remove small cell lung cancers that are so early they have not spread? In fact, there are some data indicating long term survival for small cell lung cancers treated with resection.

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