Because the central question of NLST was whether mortality due to lung cancer was reduced by screening with LDCT as compared to conventional chest x-ray, it was essential to confirm and collect data on all deaths among study participants during the trial. It was also necessary to be certain whether lung cancer was the cause of death. Mortality data is available through two timepoints, namely, Active Follow-up (Dec. 31, 2009), and Extended Follow-up (Dec. 31 2015).
Active Follow-Up (Dec. 31, 2009)
Data on all deaths were obtained from death certificates.
NLST Screening Centers first learned about the occurrence of deaths from three main sources:
- Study update forms were mailed to each active participant's address on an annual or semi-annual basis. If the participant had died, relatives or the postal service often notified the centers of the death. If no such notification was received, centers attempted follow-up contact with the participant and learned about more deaths that way. Some centers also consulted the Social Security Death Index or obituaries in conjunction with the study update forms.
- Newsletters and birthday cards mailed to participants sometimes prompted a notification of death from a participant's relative.
- A National Death Index (NDI) Plus search was conducted annually for participants who had not responded to repeated attempts to contact them.
Once the centers were aware that deaths had occurred, they obtained death certificates from state vital statistics bureaus and shipped them to centralized facilities for data compilation. All cause of death information listed on the death certificate was coded (in ICD-10), and a single underlying cause of death was determined by rules established by the National Center for Health Statistics.
After the death certificate information was added to the study database, the centers learned of some cancer diagnoses that had not previously been documented. The centers requested medical records for these cancers and performed medical record abstraction. After all cancer ascertainment activity was complete for a participant, the Endpoint Verification Process was begun.
Endpoint Verification Process (Active Follow-up Only)
EVP determined definitively whether lung cancer was the cause of death.
The Endpoint Verification Process (EVP) was designed to determine whether lung cancer, screening, or treatment caused or contributed to a participant's death. Only those participants whose study data indicated possible death from lung cancer were selected to undergo EVP review. Such participants included:
- Those with a confirmed diagnosis of cancer of the lung, cancer of a nearby site, primary cancer of a typical metastatic site of lung cancer, cancer with unknown or ill-defined site, or cancer of uncertain behavior.
- Those whose death certificate indicated cancer of the lung, cancer of a nearby site, primary cancer of a typical metastatic site of lung cancer, cancer with unknown or ill-defined site, cancer of uncertain behavior, adverse effects of health care, or unknown underlying cause of death.
- Those who died within 60 days following certain diagnostic procedures.
- Those who died from COPD at any time following certain diagnostic procedures.
- Those who died within 6 months of an NLST screening exam with a positive result or a result of negative with clinically significant abnormalities.
The EVP consisted of a review of medical records by a panel of expert physicians who reached conclusions about the cause of death. The process is further described in a publication.
Extended Follow-Up (Dec. 31, 2015)
Additional follow-up beyond the trial endpoint of December 31, 2009, is available. Extended follow-up is available through December 31, 2015.
After the active follow-up period (Dec. 31, 2009), participants were followed only passively through linkages with the NDI. Linkages were performed using probabilistic linkage methods. All but one centers were able to be linked. The personally identifiable information NLST had available for linkage included Social Security Number, full name (for some screening centers), date of birth, and sex.
Mortality follow-up was through the end of 2015 for centers with NDI linkage (comprising 97.8% of trial participants) and through the end of 2009 for the one center without NDI linkage.
Two datasets on this Web site contain mortality data. The Participant dataset should be sufficient for most analyses of mortality from any cause. The additional Cause of Death dataset contains ICD-10 codes for the EVP cause of death and for every condition listed on the death certificate (underlying COD, immediate COD, antecedent COD, other significant conditions) only for active follow-up.
(Active and Extended Follow-up)