Currently, there is no medication approved by the FDA for the adjuvant treatment of DCIS. DCIS accounts for nearly 20 per cent of all newly diagnosed breast cancer cases.

"If approved for this indication, NOLVADEX's effectiveness will have been demonstrated across several stages of the breast cancer continuum from risk reduction in women at high risk to advanced breast cancer," said Gerard Kennealey, Vice President of Medical Oncology.

DCIS is a non-invasive breast cancer involving only the cells lining milk ducts in the breast with no evidence that the disease has spread outside of these ducts. Until the 1980's, DCIS was treated by mastectomy. Today, options also include lumpectomy, or the preferred method of lumpectomy plus radiation therapy.

The FDA submission was based on data from a study, B-24, conducted by the National Surgical Adjuvant Breast and Bowel Project (NSABP). The study, published in the June 12, 1999, Lancet included 1,804 women with DCIS who had a lumpectomy and radiation therapy. Half of those patients were prescribed tamoxifen and half received a placebo. After an average follow-up period of more than five years, the researchers found that the addition of tamoxifen to the treatment regimen significantly reduced the five-year incidence of invasive cancer in the same breast by 44.8 percent (29 cases on placebo vs. 16 cases on tamoxifen - p<0.04).

Additionally, the researchers analysed the occurrence of all new breast cancer events including contralateral (in the opposite breast) breast cancer and new non-invasive breast cancers. They found that the addition of tamoxifen reduced the five-year incidence of a new breast cancer by 31.7 per cent (104 cases on placebo vs. 71 cases on tamoxifen - p<0.007).

Physicians regard DCIS as a clinical "marker" indicating that changes are occurring in a woman's breast that could lead to invasive cancer. For this reason, the goal of treatment for DCIS is not only to treat the disease itself, but to also address a woman's risk status for developing future invasive lesions in the same or opposite breast. If DCIS cells travel beyond the ducts into the surrounding tissue, they become invasive breast cancer.