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The NSABP B-24 trial (42) compared excision plus radiotherapy to excision, radiotherapy, and tamoxifen. Patients who received tamoxifen had a decreased incidence of breast cancer events (invasive or noninvasive ipsilateral or contralateral breast cancer) compared with patients who did not receive tamoxifen (8.2% vs. 13.4% at 5 years, respectively; p = .0009), but no survival benefit was found. Tamoxifen therapy resulted in a 44% reduction in the risk of subsequent invasive tumor recurrence but had no significant effect on ipsilateral noninvasive breast recurrence (Table 52.4). Positive tumor margins were significantly associated with breast recurrence, and tamoxifen reduced ipsilateral breast failure by 22% with negative margins and 44% in cases with positive or unknown margins.

In contrast to the findings of the NSABP B-24 trial, the UKCCCR trial found that tamoxifen had no effect in reducing local recurrence rate when combined with whole-breast radiation therapy (Table 52.4). When used as single agent without radiation therapy after lumpectomy, tamoxifen had no effect on the incidence of invasive recurrence but did show a statistically significant reduction in the risk of DCIS recurrence (10% vs. 6%; p = .03) (59). As such, the role of tamoxifen for DCIS in the absence of whole-breast radiotherapy remains to be defined.

Because DCIS is a precursor to invasive breast cancer and shares many biologic features of invasive carcinoma, it is increasingly recognized as a target for preventive measures. In the largest trials of the prevention of primary breast cancer among women at high risk for breast cancer by virtue of age, family history, or prior benign breast disease, tamoxifen reduced the risk of DCIS by 50% to 70% (27,40).