Dr. Aju Mathew talks about the use of and selection of patients for low-dose CT scan as a screening measure in the Indian context for saving lives that may possibly be lost to lung cancer.

Recently, the United States Preventive Services Task Force recommended yearly low-dose CT scan screening for lung cancer in persons who have significant smoking history. In 2017, the European Union had recommended that countries should plan to implement lung cancer screening. Both recommendations were based on trials that showed that low-dose CT scan screening ‘saves’ lives. But the devil is in the detail.

Before we discuss the detail, let me summarise two landmark trials.

1. First, the National Lung Screening Trial (NLST) from the United States of America: It randomised persons between 55 and 74 years of age with 30 pack-year smoking history (ex-smokers are eligible as long as they quit within 15 years) to annual screening CT scans for 3 years versus a one-time chest X-ray. The trial found a 20% relative risk reduction for lung cancer-specific mortality with CT scan screening.
2. Second, the NELSON trial from Netherlands: It randomised persons between 50 and 74 years of age who smoked more than 10 cigarettes per day for more than 30 years or more than 15 cigarettes per day for more than 25 years to undergo CT screening at various time intervals versus no-screening. There was a 24% relative reduction in lung cancer-specific mortality in patients who have undergone screening compared to those who did not.

Now, let me come to the fine print. We must screen more than 300 individuals with three annual CT scans to save one life from dying from lung cancer over 5 years (absolute risk reduction in the NLST). One in four persons who truly do not have lung cancer will get an abnormal CT scan report (false positive rate). One in forty persons who get an abnormal CT scan report will undergo an invasive procedure. Besides all of these, the screening procedure did not result in all-cause mortality reduction.

Clearly, the recommendation for low- dose CT screening for high risk individuals is not without a potential for harm. However, we should not throw the baby out with the bathwater. There is scope for improvement in how we do these scans. For instance, the method of measurement of nodules may help skew the field to a more favourable proposition.

NELSON used a volume-based measurement protocol for the nodule management whereas the NLST used a diameter-based technique. It dramatically improved the positive predictive value (chance that the positive finding is truly a cancer) from 4% in NLST to 44% in the NELSON.

In summary, the two landmark trials that showed a benefit for lung cancer mortality reduction via low dose CT scan screening also found significant potential for harm. Therefore, as cliched as it sounds, the benefits should be carefully weighed against the risks before we recommend the test to a person with high risk for lung cancer.

In an Indian or low-middle income country setting, should you recommend it? If so, who should consider doing it?

In my opinion, a person who meets all the conditions stated below may be counseled on the availability of lung cancer screening through CT scan:

• Considerable tobacco smoking exposure
• At least 5-10 years of life expectancy
• Excellent functional status
• No significant comorbidities
• Can comprehend the potential risks for CT scan screening
• Have access to a healthcare facility that has the technology and skills to do image-guided biopsy
• Willing to undergo biopsy or further imaging evaluation
• Willing to undergo cancer treatment if it is diagnosed
• Can afford the financial burden

I am yet to see someone who fits all the above criterion.

Disclaimer- The views and opinions expressed in this article are those of the author's and do not necessarily reflect the official policy or position of M3 India.

The author, Dr. Aju Mathew is a Senior Consultant Medical Oncologist at Kochi.