New perspective on cancer of the contralateral breast: a marker for assessing tamoxifen as a preventive agent.

For most of this century, when a woman has had a primary breast cancer, issues have been raised regarding her opposite (contralateral) breast. One major and persistent consideration relates to how frequently a contralateral breast cancer might be expected to occur. Vigorous debate questions whether a woman's risk for such an event might be considered great enough to justify a prophylactic mastectomy or, at least in some circumstances (e.g., when the primary tumor is a lobular invasive cancer), whether a random biopsy of the contralateral breast should routinely be done. Deliberations have also taken place regarding how to distinguish between a metastatic lesion and a second primary tumor in the contralateral breast; whether the prognosis of a patient who has had a breast cancer is altered when a new primary tumor appears in the opposite breast; whether the first and second primary tumors were synchronous in origin but metachronous in expression or whether they were metachronous from their inception; and whether radiation therapy after removal of a primary tumor by mastectomy or lumpectomy increases the incidence of contralateral breast cancer.