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Side Effects Of Tamoxifen After 5 Years

Side Effects Of Tamoxifen After 5 Years

Hormonal Therapy for Pre-menopausal Women with Early Stage Breast Cancer

Anna Mazzucco, PhD, Brandel France de Bravo, MPH, Caroline Halsted, Danielle Shapiro, MD, MPH, and Diana Zuckerman, PhD, Cancer Prevention and Treatment Fund

Breast cancer is the most common type of cancer in women around the world, and the second leading cause of cancer deaths among U.S. women. The survival rate for early-stage breast cancer is very high.  For women whose breast cancer is diagnosed before it has spread, the 5-year survival rate is 99%.  For women whose breast cancer has spread to the lymph nodes, the 5-year survival rate is 85%.

Women who are diagnosed with early-stage breast cancer almost always undergo surgery to remove the cancer (either lumpectomy/partial mastectomy or mastectomy). Most will also choose at least one other treatment in addition to surgery:

1) If they have a lumpectomy, they often undergo radiation either to shrink the tumor before surgery or to kill any cancer cells in the breast that were missed during surgery.

2) If their cancer is estrogen receptor positive (about 84% of breast cancers), many women will try to take hormonal therapy for at least five years after surgery to lower the chance of cancer in either breast in the future. For pre-menopausal women, the standard treatment is tamoxifen.[1]

Types of Hormonal Therapies for Early Stage Breast Cancer

Hormonal therapy (also called endocrine therapy or anti-estrogen therapy) is the opposite of the type of hormones women sometimes take to reduce the symptoms of menopause. It lowers your estrogen levels instead of increasing them.

Hormonal therapy is recommended for most women with breast cancer, and sometimes it is taken by women who have not been diagnosed with breast cancer but are at high risk for it based on their genes or family history. When hormonal therapy is used before breast cancer develops, it is called “primary prevention” or “chemoprevention.” Chemoprevention is completely different from the drugs used in chemotherapy to treat breast cancer. See our article on breast cancer prevention.

How Does Hormonal Therapy Work?

Tamoxifen is a selective estrogen receptor modulator (SERM), which means it blocks estrogen in breast tissue, but promotes it in other tissues (such as in bone and the inner lining of the uterus). Tamoxifen is only effective in breast cancers that are estrogen receptor positive.

Benefits of 5-Year Therapy

Does tamoxifen prevent breast cancer recurrence?

A landmark report showed that about 26% of women taking tamoxifen for 5 years after their cancer was removed had a breast cancer recurrence within 10 years, compared to about 40% of women not taking tamoxifen.[6] In that study, women with early-stage breast cancer includes women with Stage 1, Stage 2, and Stage 3A; in other words, it ranges from a very tiny breast cancer to a large cancer that has spread to several lymph nodes.  The researchers defined breast cancer recurrence as the first appearance of any breast cancer including, cancer in the same breast, cancer in the opposite breast, or distant spread of cancer. However, women who took tamoxifen for 5 years had a 0.6% chance per year of having their breast cancer return in the same breast (this is called local recurrence) compared to a 1.1% chance per year in women who did not take tamoxifen.

Benefit Even Greater Years After Therapy

The data come from the IBIS-1 study, a placebo-controlled trial coordinated by Cancer Research UK and conducted in 7145 healthy women at high risk for breast cancer. Results after 5 years of therapy, released in 2002, showed that tamoxifen reduced breast cancer by about a third.

Now the results at 10 years, including 5 years after therapy was stopped, show a 29% reduction in all cases of breast cancer (142 cases in the tamoxifen group vs 195 cases in the placebo group; P = .002) and a 34% reduction in estrogen-receptor positive (ER+) tumors (87 with tamoxifenvs 129 placebo).

The effect on the overall rate of breast cancer “is just as big at 10 years as it was at 5 years,” Dr. Cuzick commented, but “the effect specifically on ER+ tumors is even bigger at 10 years than it was at 5 years.” He presented the data in terms of a percentage decrease in incidence, as shown in the tables.

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