This study has quantified the accuracy of reported family history of cancer in two important groups of people—namely, those with colorectal cancer and those from the general population. Because we confirmed cases reported to have colorectal cancer and also identified cases that had not been reported by the interviewee, we have been able to systematically assess overall accuracy of reported family history of large bowel malignancy.
Using this approach we have determined the accuracy of reporting of colorectal cancer in a large data set comprising 332 interviewees and 5637 first and second degree relatives. We showed conclusively that substantial underreporting of cancer family history is evident in reports made at interview. In this study, the family history documentation was optimal as a trained genetics nurse conducted interviews during a lengthy consultation at the interviewee’s home. Reporting inaccuracies may be more extreme where family history is taken in a busy gastroenterology, surgical, or general practice clinic.
A comparable approach to assessing accuracy of reporting of colorectal cancer, which includes identification of unreported cases as well as checking the accuracy of cases reported at interview, has been employed in one previous study.5
This study estimated the sensitivity of reporting a family history of colorectal cancer in FDRs as 0.65 (95% CI 0.39, 0.85) for colon cancer cases and 0.81 (95% CI 0.54, 0.95) for controls, and the authors concluded that subjects were able to accurately report family history.5
However, this previous study did not consider SDRs, and no information is provided regarding the total number of relatives involved. Furthermore, the focus of this paper was on validation of an epidemiological study. The observed values for sensitivity of reporting may be less acceptable for genetic risk assessment where the objective is to determine the need for clinical intervention, particularly given the wide confidence intervals.
In general, there is a distinct lack of quality data regarding the accuracy of reporting of family history of colorectal cancer at interview, and the impact of inaccuracy and underreporting on genetic risk assessment has not been evaluated. The current study is thus highly relevant, particularly given the current increase in public demand for information on genetic risk.
We did not observe any difference in the accuracy of family history reporting in cases compared with controls. Similarly, age and sex of interviewee had no significant effect on accuracy. Clearly, the accuracy of reporting of family history by colorectal cancer cases is an important consideration as cancer occurrence is frequently the first point of contact with a particular family. This study addresses the hypothesis that individuals who have had colorectal cancer may be more likely than controls to provide false positive reports of the condition in their relatives. However, we found no evidence to support this hypothesis as there were 21 false positive reports among 199 cases compared with 11 false positive reports among 133 interviewed controls.
Table 1 shows that interviewees could provide no useful information for approximately half of all SDRs but did have some knowledge of the health status of all but approximately 5% of FDRs. This consistent disparity suggests that many instances in which cancer in SDRs goes unreported are due to lack of contact with relatives, rather than ignorance of diagnosis in a known family member. The observation that positive predictive value is similar in FDRs and SDRs lends further support to this notion. Clearly, one would expect that interviewees would have greater knowledge about FDRs, and would be more likely to receive and maintain knowledge of a cancer diagnosis from such close family. Disparity between FDRs and SDRs is evident throughout this study, and is consistent with findings from other published studies.7–10
There is some potential for bias within this study but we feel that the effect of such bias is minimal. The total proportion of potential participants who declined to take part in the study, or did not respond to a letter of invitation, was less than 20%. False positive and false negative rates were low for the record linkage process that we used, emphasising the overall validity of our approach. Spouses of cases may be more aware of their own family history of colorectal cancer than the general population, although any such effect would only apply to a small proportion of control subjects. Some mismatching may have occurred, and a proportion of relatives, probably approximately 10%, may have been untraceable. This latter effect would theoretically lead to an underestimation of the positive predictive value. However, no cases and only one control subject reported colorectal cancer in a relative reported to live abroad or deemed to be untraceable, and consequently this effect will have little influence on the reported results.
The accuracy and completeness of cancer registry data itself is a crucial consideration for any study that uses such a resource to validate or confirm diagnoses. The Scottish Cancer Registry was initiated in 1958, and ascertainment was considered to be suboptimal prior to 1968. Although ascertainment of any registry is unlikely to reach 100%, methods of ascertainment have steadily improved since this time, and the Scottish Cancer Registry is considered to be reasonably complete in recent years and to compare favourably with other registries.23
An evaluation of the accuracy of colorectal cancer registration data found that while misclassifications do occur at a low level, such data exhibit a high degree of accuracy.24
Colorectal cancer cases occurring prior to the availability of an effective cancer registry were only identified by this study if this malignancy was recorded as a cause of death. Again, this is unlikely to introduce systematic bias, but may have resulted in a slight underestimation of the positive predictive value. Overall, therefore, we consider record linkage with the Scottish Cancer Registry to constitute a reliable and valid means of determining the actual cancer experience of our study subjects. The intermediate use of central records to confirm or correct reported information and to extend knowledge of pedigrees was essential to ensure that study data were of sufficiently high quality for record linkage.
From a clinical perspective, the information provided about the family as a whole is more important than the accuracy of individual reports. The observation in this study that only two of six families who actually met surveillance criteria were identified at interview is a particular concern, implying that reliance on interview data in a clinical context could result in many families who actually meet criteria for significant family history being overlooked. Conversely, of five families reported at interview to meet the chosen criteria, only two were confirmed by record linkage to meet this classification. In practice, such an effect could lead to surveillance being applied unnecessarily. While the numbers involved are too low to provide a conclusive assessment of the clinical utility of family history information reported at interview, our results illustrate that incomplete or inaccurate interviewee reporting could have a substantial impact on genetic risk assessment.
The appropriate family history criteria for offering genetic counselling, colonoscopic surveillance, or genetic testing is the subject of much current debate, and is likely to remain so. The findings of our study are highly relevant to this discussion, as they suggest that family history information obtained by interview may be misleading, and that verification of both positive and negative interviewee reports should be conducted whenever possible.