Landmark studies that may change the treatment standards for breast cancer

Dec 14 2004

The 27th Annual San Antonio Breast Cancer Symposium that took place December 8-11 included the presentation of several landmark studies that may change the treatment standards for breast cancer.

New results from patient trials indicated that aromatase inhibitors are a better option than tamoxifen, the current standard therapy, to prevent recurrence in postmenopausal women with hormone-responsive breast cancer. Other studies showed that radiation therapy may not be necessary for older women, and that a simple blood test may identify women who will benefit from chemotherapy.

Aromatase inhibitors deplete circulating estrogen in postmenopausal women, shutting down an important cellular pathway needed for the development of breast cancer. Tamoxifen, in comparison, affects breast cancer by interacting with hormone receptors on the cell surface. The ATAC trial (Arimidex [anastrozole], Tamoxifen, Alone or in Combination) showed that when the aromatase inhibitor anastrozole was given instead of tamoxifen to postmenopausal women with early stage, hormone responsive breast cancer, the women were less likely to have breast cancer recurrence, had a longer period of time before recurrence, and were less likely to develop cancer in the other breast. Reports from the ABCSG 8 and ARNO 95 trials carried out in Germany and Austria showed that if the patients were already taking tamoxifen, they were less likely to have a recurrence if they switched to anastrozole after 2 years on tamoxifen, rather than remaining on tamoxifen.

The current treatment standard for women with low-risk breast cancer (small, node-negative tumors that are responsive to hormones) is breast conserving surgery (lumpectomy) followed by six weeks of radiation therapy and (usually) tamoxifen. A study from Dr. David McCready at Princess Margaret Hospital in Toronto showed that even if the radiation therapy was omitted, women over the age of 60 with very small tumors (approximately one-half inch in diameter or less) had extremely low recurrence rates -- 1.2% at 5 years and 3% at 8 years. These rates are slightly higher than those seen in women who received radiation therapy (where no recurrences were seen), but in absolute terms, they are quite low. Based on these findings, Dr. McCready suggested that women over the age of 60 with low-risk breast tumors may consider treatment with tamoxifen only, avoiding the physical and emotional difficulties of radiotherapy.

Because there are significant side effects associated with most drugs used to treat breast cancer, the identification of breast cancer patients who will benefit from chemotherapy is extremely important. The Oncotype DX(TM) Recurrence Score Assay, developed at Genomic Health Inc. in Redwood City, CA, measures the expression of 21 genes in a sample of peripheral blood, and converts the measurement into a score that may predict which patients will benefit from tamoxifen or chemotherapy. The test also appears to be better at predicting patient prognosis than standard analyses based on tumor size, patient age, and degree of tumor differentiation.

These studies are a small fraction of the nearly 700 oral and poster research presentations that were made at the 27th Annual San Antonio Breast Cancer Symposium, which is the largest conference in the world targeted primarily at physicians and scientists involved in breast cancer treatment and research. SABCS began in 1978 with a one-day course attended by 141 physicians from a five-state area and has now grown to a four-day symposium that this year attracted 6,806 registrants from around the world.