In total, 314 patients were eligible for enrollment (200 cases; 114 controls), and 296 patients (94%) completed the questionnaire (188 cases; 108 controls). Of these, 194 patients (142 cases; 52 controls) provided either tumor-adjacent or iliac crest bone for assay of fluoride content in bone. Eighteen patients were deceased, did not complete the questionnaire, or were otherwise lost to follow-up (12 cases; six controls). In total, 257 bone specimens were analyzed for fluoride content (200 tumor-adjacent bone; 57 iliac crest bone). Bone from six patients (five cases; one control) had fluoride levels below 100 mg F/kg, and thus were considered to be tissue other than bone (G. Whitford, personal communication).
Among patients who provided bone, there were no differences between cases and controls in enrollment site, race/ethnicity, patient’s and mother’s education level, combined household income, and whether they ever lived in an urban area. The median age of controls was higher than that of cases (p < 0.001); gender-specific age differences were also significant, with controls being older, on average, than cases for both males (p < 0.001) and females (p = 0.02) (). There was a greater proportion of male cases than female cases (p = 0.03), and fathers of cases were significantly more likely to have higher education levels than those of controls (p = 0.02) (). Comparisons between all subjects who provided bone specimens versus those who did not are included in the Appendix Table 1.
Patient Characteristics of Osteosarcoma Cases (N = 137) and Tumor Controls (N = 51) Who Provided a Bone Specimena
Among the 53 cases who provided both tumor-adjacent and iliac crest bone specimens, there was a significantly higher fluoride concentration in iliac crest bone than in tumor-adjacent bone (median = 697 vs. 558 mg F/kg bone ash, p < 0.001) (). However, when all specimens of tumor-adjacent bone (N = 137) and iliac crest bone (N = 54) from cases were included, the median fluoride concentrations in iliac crest bone were not significantly higher than those in tumor-adjacent bone (median = 695 vs. 611 mg F/kg bone ash, p = 0.10) (). In a validation study examining the fluoride content between iliac crest bone and tumor-adjacent bone among cases, the Spearman correlation was 0.61 (p < 0.001).
Figure. Box plots of interquartile range (IQR), range, and median fluoride concentrations (mg/kg bone ash). (A) Tumor-adjacent bone vs. iliac crest bone among cases that contributed both samples: IQR = 407.0-746.5 vs. 538.0-863.0; range = 121.0-1859.5 vs. 318.5-3732.5; (more ...)
There was no significant difference in the median fluoride concentration in bone between the matched osteosarcoma case and tumor control pairs (N = 32) (median = 804 vs. 714 mg F/kg of bone ash, p = 0.63) (). When bone specimens from all cases (N = 137) and controls (N = 51) were included in an unmatched analysis, the median bone fluoride concentration in tumor-adjacent bone was significantly higher in controls than in cases (median = 754 vs. 611 mg F/kg of bone ash, p = 0.01) ().
There were no differences in the results of the conditional and unconditional analyses; thus, the results of the unconditional analyses are reported given the increased power for detecting associations with bone fluoride. In the age- and sex-adjusted analysis, OR = 1.22 for an increase in bone fluoride from the 25th percentile (463.5 ppm) to the 75th percentile (943.3 ppm), representing an OR = 1.32 (95% CI, 0.58-3.03) for a 1-unit increase in the natural log of fluoride (ppm). After adjustment for age and gender, history of broken bones, other bone diseases, other cancer diagnoses, and history of receiving radiation prior to illness were significant covariates (see Appendix Table 2). The OR for log bone fluoride adjusted for these predictors, age, and gender was 1.23 (95% CI, 0.51-2.97) (). With a stepwise selection method to determine the final model adjusted for age and gender, a history of broken bones remained as a significant predictor, and the final adjusted OR was 1.33 (95% CI: 0.56-3.15) ().
Odds Ratios and 95% CI for a 1-unit Increase in Natural Log of Fluoride Concentration (ppm) in Bone and Risk of Osteosarcoma: (A) for All Osteosarcoma Cases and Tumor Controls and (B) among Patients under 45 Years of Age
In an analysis restricted to patients < 45 yrs old (123 cases; 30 controls), history of broken bones was the only predictor of osteosarcoma risk at the p = 0.25 level, adjusted for age and gender. However, the final risk-adjusted model included only age and gender (OR = 1.23, 95% CI: 0.48-3.16) ().