To the Editor: Dr Chan and colleagues1 studied the association between self-reported family history of colorectal cancer and survival in a cohort of patients with stage III colorectal cancer receiving adjuvant chemotherapy. Their conclusions were that cancer recurrence was lower and survival greater in patients with a positive family history. We believe that a flawed study design precludes reaching these conclusions.
The first concern is the absence of data on the persons who were not included or who were excluded. Data are available only for stage III colorectal cancer patients. The cancer stage and family history distribution in the original population might have differed extensively, which could account for the differences in cancer recurrence between the groups with and without family history. Also, persons who died of colorectal cancer before family history data could be collected were excluded. Although this was a small group, if a significant proportion of these excluded patients had a positive family history, this might have caused a substantial shift in the survival curve.
Ascertaining the family history of colorectal cancer solely by unsubstantiated self-report questionnaires leads to invalid information. Many persons are unaware or incompletely aware of sporadic cases of colorectal cancer in their family. Persons who were aware of these cases may have tended to follow a more health-conscious lifestyle and be more alert for symptoms of colorectal cancer. They may have been more adherent to screening colonoscopy than average,2 which could have led to cancer being detected in earlier stages.3 Therefore, the remaining stage III colorectal cancer patients with family history may on average have had more aggressive tumors that usually are more responsive to chemotherapy. This hypothesis is substantiated in one of the references cited by Chan et al, in which patients with a positive family history were significantly younger.4 In the study by Chan et al, the patients with a family history were older than the patients without a family history, which might indicate that a substantial proportion of patients with less aggressive colorectal cancer were already diagnosed at a younger age.
Second, the authors did not collect data on the number of persons comprising the immediate family and the age and sex of the family members. The frequency of family history of colorectal cancer should have been analyzed based on the number of person-years in the family and adjusted for sex differences.
Financial Disclosures: None reported.
Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature
Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal
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