**Core Concept**
Gynecomastia is a benign enlargement of breast tissue in males, often resulting from an imbalance between estrogen and androgen levels. The investigation of gynecomastia involves assessing various hormone levels to identify the underlying cause.

**Why the Correct Answer is Right**
When investigating gynecomastia, clinicians typically measure levels of testosterone, luteinizing hormone (LH), follicle-stimulating hormone (FSH), and estradiol (E2) to determine the hormonal cause. Testosterone levels help assess androgen deficiency or resistance, while LH and FSH levels evaluate the pituitary-gonadal axis. Estradiol levels are measured to assess estrogen production. However, the estimation of **thyroid-stimulating hormone (TSH)** is not directly relevant to the investigation of gynecomastia, as thyroid hormones do not typically cause gynecomastia.

**Why Each Wrong Option is Incorrect**
* **Option B:** Estimating thyroid-stimulating hormone (TSH) levels is not directly relevant to the investigation of gynecomastia.
* **Option C:** While thyroid hormones do not typically cause gynecomastia, they may be measured in the context of a broader endocrine evaluation.

**Clinical Pearl / High-Yield Fact**
When investigating gynecomastia, remember to consider the patient's overall endocrine status and potential causes of hormonal imbalances, such as testicular tumors, liver disease, or certain medications.

**Correct Answer:** B.