**Question:** Long term adverse effect of tamoxifen is

A. Increased risk of endometrial cancer
B. Decreased libido
C. Osteoporosis
D. Breast cancer

**Core Concept:** Tamoxifen is a selective estrogen receptor modulator (SERM) used to treat and prevent breast cancer. While it is effective in reducing breast cancer risk, it has potential side effects.

**Why the Correct Answer is Right:** Tamoxifen primarily acts as an antiestrogen in the breast tissue, blocking estrogen action and preventing estrogen-dependent cell growth. However, in the endometrium, tamoxifen acts as a weak estrogen agonist, increasing the risk of endometrial cancer.

**Why Each Wrong Option is Incorrect:**

A. Tamoxifen does not increase the risk of breast cancer; in fact, it is used to treat and prevent breast cancer.
B. Tamoxifen can cause hot flashes and other menopausal symptoms, but it does not significantly affect libido.
C. Tamoxifen can cause an increase in bone resorption and decrease bone density, which is considered a breast cancer risk factor, but it does not directly cause osteoporosis.
D. Tamoxifen does not cause an increased risk of osteoporosis; it is actually used to prevent osteoporosis in certain patients.

**Clinical Pearl:** Tamoxifen has well-established benefits in breast cancer treatment and prevention, but it is essential to weigh the potential risks, such as endometrial cancer, against the potential benefits for individual patients.

**Correct Answer:** A. Increased risk of endometrial cancer