Overview: Approximately 25% of breast cancers in the United States are diagnosed as ductal carcinoma in situ (DCIS). Rates of DCIS have risen from 5.8 per 100,000 women in the 1970s to 32.5 per 100,000 in 2004. This pattern is generally attributed to increased use of screening mammography. DCIS is a major risk factor for invasive breast cancer, and considerable controversy remains about whether DCIS should be considered a direct precursor of invasive breast cancer. There is, however, a general consensus that DCIS represents an intermediate step between normal breast tissue and invasive breast cancer. Although the majority of major risk factors are similar for DCIS and invasive breast cancer, prognostic factors including estrogen and progesterone receptor status and HER2 positivity are less well studied but look to have similar value in both cases. The use of postdiagnostic MRI, sentinel lymph node biopsy, surgery, radiation, and endocrine therapy are all evolving as evidence from randomized and observational studies continues to accumulate. Treatment of DCIS requires a balance between risk of overtreatment and undertreatment. Ongoing studies are focusing on whether partial-breast irradiation is as effective as whole-breast irradiation and whether treatment with endocrine therapies can reduce the likelihood of either invasive breast cancer or DCIS recurrence. In general, treatment decisions should take into account the likelihood that an apparent case of DCIS could harbor foci of invasive disease.
Lifestyle Factors and the Risk of a Second Breast Cancer after Ductal Carcinoma In Situ
