Medical Statistics at a Glance
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Chapter 33, Question 1.
Odds ratios in a breast cancer case-control study

Using a population-based sample of women, McCarty and colleagues1 conducted a case-control study to identify genetic factors associated with the development of breast cancer. Of particular interest was the presence of multiple polymorphisms in the GST gene (GSTA1, GSTM1, GSTP1, GSTT1). In multivariable analyses, cases (those recently diagnosed with breast cancer) were 10% more likely than matched-controls to possess 3 or more of the variant alleles (odds ratio [OR] 1.10, 95% confidence interval [CI] 0.77, 1.57). The OR was 1.56 (1.13, 2.16) among women with detectable PAH-DNA adducts but 0.93 (0.56, 1.56) among women without detectable adducts (P-value for interaction: 0.43). Among ever smokers, the OR was 1.18 (0.82, 1.69) whereas it was 1.44 (0.97, 2.14) among never smokers (P-value for interaction: 0.62).

1. McCarty, K.M., Santella, R.M., Steck, S.E., Cleveland, R.J., Ahn, J., Ambrosone, C.B., North, K., Sagiv, S.K., Eng, S.M., Teitelbaum, S.L., Neugut, A.I., and Gammon, M.D. (2009) PAH-DNA adducts, cigarette smoking, GST polymorphisms, and breast cancer risk. Environ. Health. Perspect. 117; 552-558.

Select all of the statements which you believe are true.

There was no evidence that possessing 3 or more of the variant alleles was associated with the risk of developing breast cancer.
There was statistical evidence that the effect of having 3 or more of the variant alleles was stronger in women with detectable PAH-DNA adducts than among women without detectable PAH-DNA adducts.
The association between 3 or more variant alleles and breast cancer was significantly stronger in never smokers than in ever smokers.
Never smokers with 3 or more three variant alleles were at increased risk of breast cancer compared to ever smokers with 3 or more variant alleles.
On the basis of these findings, genetic screening for breast cancer should not be targeted to never smokers and those with detectable PAH-DNA adducts.