Detection of contralateral breast cancer by mammography in women with previous breast cancer and the impact of endocrine therapy.

Aims: To determine the efficacy and extent of screening mammography for detection of contralateral breast cancer in a cohort of women with previous unilateral mammary carcinoma, and to assess the effect of endocrine therapy on the risk of developing cancer in the contralateral breast.

Methods: Women with previous breast cancer eligible for mammography were identified from the Auckland breast cancer data file and the extent and outcome of mammographic screening determined by questionnaire and survey of mammography reports. The extent of adjuvant hormonal therapy and development of contralateral breast cancer was ascertained from the ABCDF records.

Results: Of 703 eligible subjects, 59% had undergone screening mammography with a cancer detection rate of 17 per 1000 mammograms and a benign to malignant ratio was 1.7 to 1. Contralateral breast cancer developed in 2.9% of 1980 women with previous unilateral mammary tumours who did not receive endocrine therapy with 1.1% of 374 women who were given adjuvant hormonal treatment (p = 0.04).

Conclusions: The efficacy of mammography in those screened was comparable to major overseas screening programs, but the proportion of women undergoing mammography in this high risk group was relatively low suggesting a need for greater promotion of mammography in Auckland. The use of adjuvant endocrine therapy significantly reduced the rate of development of contralateral breast tumours supporting the current development of formal trials of chemoprevention of breast cancer in women at high risk groups of the disorder.