**Core Concept**
Galactorrhea, amenorrhea, and weight loss are symptoms of hyperprolactinemia, a condition characterized by elevated levels of prolactin in the blood. This can be caused by various factors, including pituitary tumors that secrete prolactin.

**Why the Correct Answer is Right**
Prolactinomas, a type of pituitary adenoma, can cause an overproduction of prolactin, leading to galactorrhea (spontaneous milk production), amenorrhea (absence of menstrual periods), and weight loss due to the metabolic effects of hyperprolactinemia. The tumor can suppress the secretion of gonadotropin-releasing hormone (GnRH) from the hypothalamus, resulting in decreased production of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) by the pituitary gland, which in turn leads to amenorrhea. The weight loss is often associated with an increased appetite and metabolic changes.

**Why Each Wrong Option is Incorrect**
**Option A:** Anorexia nervosa (B) is a psychological eating disorder characterized by restrictive eating, which can lead to amenorrhea, but it is not typically associated with galactorrhea or weight loss due to hyperprolactinemia.

**Option B:** Hypothyroidism (C) can cause amenorrhea, but it does not typically cause galactorrhea. Additionally, weight loss is not a common feature of hypothyroidism.

**Option C:** Hypothalamic causes (D) can lead to amenorrhea, but they do not typically cause galactorrhea or weight loss due to hyperprolactinemia. Hypothalamic dysfunction can disrupt the normal feedback mechanisms that regulate prolactin secretion.

**Clinical Pearl / High-Yield Fact**
Prolactinomas are a common cause of hyperprolactinemia and can be effectively treated with dopamine agonists, such as bromocriptine or cabergoline, which reduce prolactin secretion by stimulating dopamine receptors in the pituitary gland.

✓ Correct Answer: A. Pituitary Cancer