lung cancer screening

Recent recommendations by the Am College of Chest Physicians to perform low-dose CT screening of smokers (see lung cancer CT screening guidelines chest 2013 in dropbox, or DOI: 10.1378/chest.12-2377). these recommendations parallel the interim recommendations of the American Lung Association (see lung cancer CT screening guidelines ALA 2012 in dropbox)

Baseline: lung cancer is common and has generally poor prognosis (esp with lesions greater than stage 1), causing as many deaths as the combo of the next four cancers. one thing to keep in mind is that there are newer therapies that work better than the old ones -- targeted to the specific tumor-associated genetic mutations engendered by the cancer (ie, possible that these new treatments could change the risk/benefit analysis of screening in the future).  of note, the arena of smoking-related morbidity is changing: tobacco companies have seen shrinking local markets (showing that sometimes after decades of obvious connection with lung cancer/persistent denial by the corporations, public health initiatives may work....); as a result,  there has been huge-scale exporting ("dumping") of cigarettes to developing nations, with likely huge increases in tobacco-related morbidity and mortality in the near future. [and, as an addition to this blog, a fundamental shift by the cigarette companies to focus on developing and advertising e-cigarettes]

Cancer prevention: attempts to prevent cancer in smokers mostly with different antioxidants or anti-inflammatories (eg b-carotene, aspirin, selenium, inhaled steroids, vitamine E, retinoids) have not panned out and are not recommended. preventing smoking initiation is the clearest prevention (though 15% of lung cancers are not smoking related. we do know, however,  from many epidemiologic studies over the decades that cancer risk geometrically increases with multiple insults, including air pollution/environmental exposures and occupational exposures in addition to smoking). for those who smoke,  smoking cessation clearly helps!, with about a 15 year lag to reducing the lung cancer risk to near non-smoker levels (unlike the heart disease risk, which decreases dramatically within 6 months of smoking cessation).

screening methods: prior studies have not shown clinical benefit with either CXR of sputum cytology screening.

low-dose CT screening (LDCT) has found lots of nodules identified in 10-50% of smokers. here is the current LDCT study by the National Lung Screening Trial Research Team (NSLT)—(see lung cancer CT screen nejm 2011 in dropbox, or 10.1056/NEJMoa1102873). details:

    --screened 27K high risk patients with LDCT and 27K with CXR yearly for 3 years and followed another 3.5 yrs

    -- found 25% with positive screen on LDCT and 7% by CXR, 

    ​--lung cancer: 645 cases/100K person-yrs with LDCT and 572/100K person-yrs with CXR --13% more. 

    --most notably, there were 247 lung cancer deaths/100K person-yrs with LDCT and 309 lung cancer deaths/100K person-yrs with CXR, a significant 20% decrease (though not very large absolute numbers – difference of only 62 deaths/100K person-yrs...), and all-cause mortality decreased 7%. 

    --the LDCT pickup of cancer was similar each of the 3 years (suggesting that it would be useful to continue screening annually). 

    --but, very large number of false positives (>95% of positives were false ones). the vast majority of those with abnormal screens had follow-up radiologic procedures, a small  minority with invasive testing (1.2% of pts not found to have cancer had a biopsy or bronchoscopy).  

    ​--BUT, given the high number of abnormal screens, the "low-dose" radiation did not remain so low. the LDCT delivered 1.5 mSv of radiation (vs 8 mSv for regular chest CT) because of the large number of positive LDCT who then received follow up chest CT or PET CT,  the average dose overall for the LDCT cohort was actually 8mSv. the rough calculation is that this degree of radiation exposure (mostly based on atomic bomb and some medical imaging studies) would create one cancer death per 2500 people screened.

    --the recommendation (from NSLT):  for smokers and former smokers aged 55-74 who have smoked >30 pack-yrs and either continue smoking or have stopped within the past 15 years should be offered annual LDCT, if comprehensive care can be provided as in the NLST trial.

so, this recommendation, at this point, is by pulmonary specialist organizations, which may have some self-interest (organizationally, or by the individuals involved in crafting the recommendations) to be aggressive (eg, as with the american urology assn and PSA screening).  we may want to wait for a more neutral group (eg USPSTF, though i suspect they will follow suit, given that the NLST is a well-done study). my fundamental concern is that at the same time we are getting recommendations about expensive, intensive, high-tech screening for a largely preventable cancer (and with a significant but low difference in absolute death rates by screening), we in the trenches are getting less and less support for programs to prevent or stop smoking (cutbacks in health educators, varying and variable insurance-based support for smoking cessation devices).  In addition, i am very concerned about the additional radiation exposure (will also resend some of my previous emails about risks of radiation exposure).

would add the following concerns (10/15/14):
1. the USPSTF extended the recommendation from the age range of 55-74 in NSLT​ to 55-80 year olds , presumably because of mathematical modeling.
2. the USPSTF extended the interval of screening from 3 years in NSLT to all who smoked 30 pack-years and currently smoke or quit within the  past 15 years (ie, with the potential that someone could get 25 annual LDCTs if they continued to smoke, with the attendant high dose followup scans in the large number who will have false positives), with the likelihood of creating additional cancers from radiation exposure (the NSLT was projected to create one cancer death per 2500 screened in just 3 years!!).
3. the basis of the USPSTF extension of screening from 3 to up to 25 years was that in the 3 years of NSLT, they kept picking up new cancers. BUT, if you look at the year-by-year pickup, there was a pretty dramatic dropoff by year 3 (goes from positive results of 27.3% in year 1 to 27.9% in year 2, then drops to 16.8% in year 3), which i think makes the potential 25 year annual screening suggestion a tad iffy...