Step 1: Review pituitary adenoma classification.
Pituitary adenomas are categorized by the primary hormone they secrete and can be functional (hormone-producing) or non-functional.
Step 2: Define lactotroph adenomas.
Lactotroph adenomas are prolactin-secreting pituitary tumors, representing the most frequent type. They lead to hyperprolactinemia.
Symptoms may include galactorrhea, amenorrhea, infertility, and hypogonadism.
Step 3: Evaluate the provided options.
- (A) Growth hormone: Indicates somatotroph adenomas, not lactotrophs.
- (B) $\beta$-TSH: A marker for thyrotroph adenomas.
- (C) ACTH: A marker for corticotroph adenomas.
- (D) Prolactin: The correct marker for lactotroph adenomas.
Step 4: Final determination.
Prolactin is the immune marker specific to lactotroph adenomas.