The National Surgical Adjuvant
Breast and Bowel Project
(NSABP) has launched a new phase III clinical trial that will evaluate
exemestane (Aromasin) in 3,000 postmenopausal women diagnosed with estrogen
receptor-positive breast cancer who have completed 5 years of tamoxifen
(Nolvadex) therapy. The trial, protocol B-33, will determine whether exemestane
will prolong disease-free and overall survival in women previously treated for
breast cancer. Over 100 sites in the United States, Canada, and Puerto Rico are
expected to take part in the trial.
Exemestane is an oral aromatase inactivator currently approved
for the treatment of advanced breast cancer in postmenopausal women whose tumors
have stopped responding to tamoxifen. This group of drugs selectively targets
and inactivates the aromatase enzyme, reducing the supply of estrogen to
cancerous cells, and thus preventing the cells from continuing to grow.
"This study could potentially ease women’s concerns
regarding breast cancer recurrence and what treatment options are available
after tamoxifen therapy is complete," said Dr. Roy Smith, director of
medical affairs and oversight at NSABP, and protocol officer for the trial.
A majority of patients treated with tamoxifen are disease-free
after 5 years of therapy. However, even after several years of tamoxifen
therapy, some of these patients harbor small tumor cells that could spread to
another part of the body and cause a recurrence of cancer.
"This trial is unique in that it offers a therapy for women
who have not had a recurrence of cancer and who have completed standard
antiestrogen therapy with tamoxifen," said Dr. Terry Mamounas, trial
protocol chair. "Sequential treatment with exemestane immediately following
tamoxifen therapy may continue to treat hormone-sensitive tumors. Tamoxifen is
the standard adjuvant hormonal therapy for women with breast cancer. However,
studies have shown that tamoxifen offers the greatest benefit when taken for
only 5 years."
In the trial, women who have completed 5 years of tamoxifen
therapy will be randomly assigned to receive either 25 mg of exemestane daily
for 2 years or placebo. The most commonly reported side effects associated
with exemestane include mild to moderate hot flashes, nausea, and fatigue.