2 ORAL Magnetic Resonance Imaging (MRI) in the preoperative assessment of patients with lobular carcinoma of the breast

Introduction: Postmenopausal women who are current users of hormone replacement therapy are at increased risk of developing breast cancer. The effect of HRT on the subsequent pathological characteristics of the tumours is unclear as data from observational studies and randomised trials do not agree. Methods: A prospective study of 622 postmenopausal women who had all been screened and diagnosed with breast cancer either at screening or in the interval between screening, was carried out within the Million Women Study with information about HRT exposure collected at recruitment via selfreporting questionnaire. HRT users were defined as those women who were either currently using HRT or had stopped HRT use in the year previous to diagnosis. HRT non-users were defined as those women who had never used HRT or have used HRT more than one year previous to diagnosis. Information about the pathological characteristics of invasive breast cancer was collected from hospital pathology record data without knowledge of HRT use. Odds ratios of the invasive tumour characteristics in relation to HRT use were calculated using a multivariate logistic regression equation. Results: Among the 622 women, 305 women were users of HRT and 307 women were non-users. The mean tumour size was significantly higher among the HRT users compared with the non-user group (18.9mm vs 16.6mm, p=0.02). The proportion of tumours with lymphovascular invasion (30% vs 21%, p=0.02) and positive axillary nodes (35% vs 25%, p=0.04) was also significantly higher among the HRT users. However following adjustment for the mode of detection i.e. screen-detection or interval cancer, on multivariate analysis no significantly increased risk of these characteristics was observed, however the risk of a grade 3 tumour was significantly lower in HRT users compared to non-users (odds ratio 0.47; 95% confidence interval 0.26-0.85; p=0.01). Conclusion: Tumours in HRT users compared to non-users are larger and more likely to have spread beyond the breast but these differences are largely explained by differences in the mode of detection with HRT users more likely to be detected with cancer in the interval between screens, as HRT is known to decrease the sensitivity and specificity of mammography.