Left-right differences in the proximal femur's strength of post-menopausal women: a multicentric finite element study

The strength of both femurs was estimated in 198 post-menopausal women through subject-specific finite element models. Important random differences between contralateral femurs were found in a significant number of subjects, pointing to the usefulness of further studies to understand if strength-based classification of patients at risk of fracture can be affected by laterality issues.

INTRODUCTION

Significant, although small, differences exist in mineral density and anatomy of contralateral proximal femurs. These differences, and their combined effect, may result in a side difference in femurs' strength. However, this has never been tested on a large sample of a homogenous population.

METHODS

The strength of both femurs was estimated in 198 post-menopausal women through CT-derived finite element models, built using a validated procedure, in sideways fall conditions. The impact of the resulting asymmetry on the classification of subjects at risk of fracture was analysed.

RESULTS

The small difference observed between sides (the right femur on average 4 % stronger than the left) was statistically significant but mechanically negligible. In contrast, higher random differences (absolute difference between sides with respect to mean value) were found: on average close to 15 % (compared to 9.2 % for areal bone mineral density (aBMD) alone), with high scatter among the subjects. When using a threshold-based classification, the right and left femurs were discordant up to over 20 % of cases (K always lower than 0.60) but the left femur was concordant (mean K = 0.84) with the minimum strength between right and left.

CONCLUSION

Considering both femurs may be important when trying to classify subjects at risk of failure with strength estimates. Future studies including fracture assessment would be necessary to quantify the real impact.

Breast Cancer Risk Single Nucleotide Polymorphism (SNP) Genotypes Do Not Correlate with Risk Estimates from Existing Prediction Models

Background:Breast cancer risk assessment professionals employ models to estimate individual probabilities of developing breast cancer. The Gail, Claus and BRCAPro models integrate personal, reproductive and family history variables to generate absolute risk estimates. A number of common DNA variants (single nucleotide polymorphisms, SNPs) are associated with modest elevations (relative risk < 2) of breast cancer risk. We investigated the correlation between genotype at 18 published risk SNPs and model-derived breast cancer risk estimates.Methods:Subjects were 475 unaffected, BRCA mutation-negative women who were evaluated for a family history of breast or ovarian cancer. At the time of testing, subjects provided information that was used to estimate absolute breast cancer risk by Gail, Claus, and BRCAPro models. Subjects were genotyped by Sequenom iPLEX MassArray (Sequenom, Inc., San Diego, CA) at loci reported to be associated with elevations in breast cancer risk (1p11.2, 2q35, 5p12, 6q22.33, 8q24, CASP8, COX11, FGFR2, LSP1, MAP3K1, RAD51L1, SLC4A7, TNRC9). Kruskal-Wallis and Spearman correlation tests were used to compare risk estimates for individuals by genotype and number of risk alleles.Results:The median age at sample donation was 46 years (range 24-83). Most subjects (94.9%) were white, and 65.5% were of Ashkenazi Jewish (AJ) ancestry. Median breast cancer risk scores risk estimates were significantly lower from BRCAPro (5 yr: 1.1%, lifetime (LT): 11.6%) than those derived from Gail (5 yr: 1.8%, LT: 18.5%) or Claus (5 yr: 1.5%, LT: 11.8%) models. No significant differences (p>0.05) in distribution of estimated breast cancer risk scores were found between women carrying 0, 1, or 2 risk alleles at any locus except 6q22.33, where AJ women homozygous for the risk allele rs2180341 were noted to have higher LT Claus (p=0.001) and BRCAPro (p=0.01) estimates. When comparing subjects with no risk alleles to those with 1-2 risk alleles for each SNP, no significant differences in distribution of estimated risk were noted at any loci, including 6q22.33. There was no significant correlation between the total number of risk alleles carried by a subject and her estimated lifetime Gail (ρ=-0.052, P=0.27), Claus (ρ=0.051, P=0.32), or BRCAPro (ρ=0.024, P=0.60) risk.Conclusions:In this analysis, risk allele genotype did not correlate with absolute breast cancer risk estimated by standard models. This suggests that the contribution to risk of genotype at these SNPs is insufficient to impact the modeled estimate. Further studies are necessary to evaluate whether incorporation of genotypic information can improve the calibration or discriminatory accuracy of existing models.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 901.

Breast cancer risks in individuals testing negative for known family mutations in BRCA1 or BRCA2

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Background: Genetic testing for BRCA1 and BRCA2 mutations in individuals from families with known deleterious mutations can identify both those at high risk of disease and those who are not. Recent studies have raised concern that women who test negative for mutations previously identified in their families (“true negatives,” TN), may nonetheless have a higher incidence of breast cancer than women in the general population. To evaluate this question, we have examined a prospectively followed cohort of TN to assess their risk of breast cancer. Methods: The women included were first and second degree relatives of known BRCA1 and BRCA2 mutation carriers, had undergone genetic testing and were negative for the known familial mutation, and were unaffected at the time of genetic testing. Standardized incidence ratios (SIR) and 95% confidence intervals (CI) were calculated using SEER incidence rates from 1992–2005. Results: Among 375 TN women followed for a mean of 4.9 years (total 1,962 person-years), 2 invasive and 2 in situ breast cancers were diagnosed. Four invasive breast cancers were expected, whereas 2 were observed, for an age-adjusted SIR of 0.52 (95% confidence interval 0.13–2.09). One case of in situ breast cancer was expected, whereas 2 were observed (SIR=2.30; 95% CI 0.57–9.19). There were no cases of ovarian cancer observed, whereas 0.4 cases were expected. Conclusions: In this prospective study of women who were unaffected at the time of genetic testing and who were negative for a known familial mutation in BRCA1 or BRCA2, no excess risk of invasive breast cancer was observed. Although we cannot exclude a modest increase in risk (RR<2), our data suggest that such women should adhere to population based guidelines for breast cancer screening.

No significant financial relationships to disclose.