The validity of self-reported cancer in a population-based cohort compared to that in formally registered sources.

Background: Self-reported cancer has been validated with heterogeneous results across populations. The aim was to assess the validity of self-reported cancer in the Lifelines population-based cohort and to search for explanations for not reporting cancer.

Methods: Data from adult participants (n = 152,780) from Lifelines was linked to the Dutch-Nationwide pathology databank (PALGA), which has nearly 100% coverage of cancer diagnoses in the Netherlands and is considered as the gold standard for ascertainment of cancer diagnosis in this study. Sensitivity and positive predictive value (PPV) for self-reported cancers -reported as hand-written free text- were described. Logistic regressions analyses were performed to evaluate whether socio-demographic factors were associated with the presence of self-reported cancer when there was a diagnosis in PALGA.

Results: 6611 (4.50%) participants had at least one self-reported diagnosis of cancer, where 9960 (6.97%) participants had at least one cancer diagnosis in PALGA. The sensitivity of self-reported cancer was 64.68% [95%CI:63.71-65.66], and 70.18% [95%CI:68.83-71.56] after excluding skin and cervical cancers. Skin and cervical cancers represented 61.24% of non-self-reported cancers. The overall PPV was 97.45% [95%CI:97.45-97.81], and 97.33% [95%CI:96.72-97.82] after the exclusion of skin and cervical cancers. Participants who did not self-report their cancer were more likely to be male, had longer time since diagnosis and lower educational level.

Conclusion: Overall, the reports of cancer in Lifelines have a high positive predictive value and moderate sensitivity. One third of the cancers were not reported, mainly skin and cervical cancers. Male participants, those with a lower educational level and those with longer time since diagnosis were less likely to self-report a diagnosed cancer.