Of mothers who returned the self-administered questionnaire, 222 of 333 (67%) case mothers and 336 of 428 (79%) control mothers had no missing items on the FFQ. The histologic subtypes of the 222 cases included 99 yolk sac tumors (36 male, 63 female), 55 teratomas (malignant teratoma, immature teratoma; 12 male, 43 female), 36 seminomas (seminoma, dygerminoma, germinoma; 2 male, 34 female), 22 other nonseminoma (embryonal carcinoma, choriocarcinoma, polyembyoma; 15 male, 7 female), 8 other (mixed germ cell tumor components; 3 males, 5 females); and 2 not specified (1 of each sex).
Demographic characteristics overall and by sex are given in . Cases and controls differed on the index child's sex; 69% of cases were female compared with approximately 58% of control children, which was expected given the different frequency matching in the sampling of male and female controls. Slightly over 50% of cases were diagnosed under the age of years. Cases tended to have both higher (>4,000 g) and lower (<3,000 g) birth weights, with cases being significantly more likely than controls, especially males, to have a high birth weight. Overall, case mothers and control mothers did not differ significantly in age or parity at the index pregnancy. However, male cases tended to have both younger (age, ≤24 years) and older (age, ≥35 years) mothers than male controls; an opposite pattern was observed among female cases. Case mothers tended to have lower levels of education and income than did control mothers and were more likely to be nonwhite. Case mothers were less likely to have used vitamin supplements during pregnancy.
Distribution of Data on Demographic Factors in a Case-Control Study of Childhood Germ Cell Tumors and Maternal Diet During Early Pregnancy, Children's Oncology Group, United States, 1993–2001a
In general, case mothers and control mothers were similar in their daily food consumption for each of the individual items on the FFQ (), although case mothers tended to consume higher quantities of chips and fried potatoes and fewer cruciferous vegetables. Of note, the means and standard deviations from the extracted dietary pattern scores indicated that cases and controls did not significantly differ in adherence on any factor score and that both cases and controls had factor scores that followed the expected standard normal distribution.
Four distinct dietary patterns were identified from the factor analysis: “Western diet,” “fruits and vegetables,” “proteins,” and “healthful” (). “Western diet” had high positive loadings for processed meats and packaged snack foods. The second pattern, “fruits and vegetables,” had high loadings for carrots, fruits, juices, green salads, and cruciferous vegetables. Eggs, bacon, pork, and fried chicken all loaded high on the third “proteins” factor. The fourth pattern, “healthful,” was composed of high loadings on foods such as skim/low-fat milk and other vegetables and high negative loadings on foods such as whole milk, processed foods, and fried chicken. The cheese product food item had moderate loadings on both the “Western diet” and the “proteins” patterns. Fruits loaded on both “healthful” and “fruits and vegetables,” although their loading was considerably higher for the latter pattern (0.61 compared with 0.30). Factor loadings for each pattern are shown in .
Factor Loadingsa of 4 Dietary Factor Patterns From Principal Components Analysis in a Case-Control Study of Childhood Germ Cell Tumors, Children's Oncology Group, United States, 1993–2001
Among controls, consumption patterns differed by race, with nonwhites adhering more to all dietary patterns except “proteins” and vitamin nonusers adhering more to both the “Western” and “fruits and vegetables” patterns (results not shown). Higher household income and maternal education were associated with greater adherence to the “proteins” pattern.
In the initial unadjusted analysis, none of the 4 factor patterns reached statistical significance, although a 1-unit increase in score for the “fruits and vegetables” factor was modestly associated with a reduced risk (odds ratio (OR) = 0.86, 95% confidence interval (CI): 0.72, 1.02) (). After adjustment for matching variables and covariates (vitamin use, parity, and birth weight), the “fruits and vegetables” pattern was inversely associated (OR = 0.83, 95% CI: 0.69, 0.99), while all other factor patterns remained unassociated with GCTs. Results for stratification by age of diagnosis (before or after age 5 years) yielded estimates in a similar direction (), although none was significant. There were also no significant associations between dietary patterns and GCTs in the female subgroup. However, analysis of the males-only subgroup showed significant decreased risk associated with GCTs (OR = 0.66, 95% CI: 0.47, 0.92) with the “fruits and vegetables” factor pattern. Further, an interaction term examining this factor pattern between age of diagnosis and the index child's sex suggested evidence of effect modification (P = 0.002), with male cases diagnosed before age 5 years showing the strongest effect.
Odds Ratios and 95% Confidence Intervals for Subgroup Analyses of the Index Child's Sex and Age at Diagnosis Among Cases (n = 222) and Controls (n = 336) From the Children's Oncology Group, United States, 1993–2001
Nonprobabilistic sensitivity analyses on the effects of nondifferential reporting error are given in . Minor to severe degrees of nondifferential reporting error did not grossly alter the results, although overreporting seemed to exert a larger influence than assumed underreporting. Thus, our results were not sensitive to various degrees of assumed reporting error.
Crude Odds Ratios Adjusted for Nondifferential Reporting Error by Dietary Factor Pattern in a Case-Control Study of Childhood Germ Cell Tumors, Children's Oncology Group, United States, 1993–2001