Breast tumors often require hormones for growth, which poses a
unique problem because the hormones involved in tumor growth are
either estrogen, progesterone, or both. Estrogen and
progesterone are naturally occurring and necessary hormones,
produced mainly in the ovaries and adrenal glands in varying
amounts throughout a woman's lifetime. These hormones are
essential for many physiological functions, such as bone
integrity. Hormone receptor-positive tumors can consist of
cancer cells with receptor sites for estrogen, progesterone, or
both. The hormones attach to receptor sites and promote cell
proliferation. Hormone therapy blocks the hormones from
attaching to the tumor receptor sites and may slow or stop the
cancer's growth. The drug most often used in this type of
endocrine therapy is tamoxifen, with a response rate from
30-60%. Other therapies are sometimes used, such as aromatase
inhibitors (that inhibit the conversion of precursors to
estrogens) or oophorectomy (the removal of the ovaries). The
stronge