Which breast cancer subtype is most commonly associated with response to endocrine therapy?

• A. Luminal B
• B. Luminal A
• C. Basal
• D. HER2-Enriched

Answer: (B)

Endocrine therapy works best when a breast cancer tumor depends on estrogen receptor signaling. Tumors that are ER-positive respond to blocking estrogen effects, and among the ER-positive subtypes, luminal A shows the strongest hormone dependence. Luminal A is typically ER-positive, PR-positive, HER2-negative, and has a lower proliferation rate, which makes these tumors particularly sensitive to endocrine therapies such as aromatase inhibitors or SERMs.

Luminal B, while also ER-positive, tends to have higher proliferation and may be HER2-positive, so its response to endocrine therapy is present but not as robust as luminal A. Basal (often triple-negative) and HER2-enriched tumors rely less on estrogen signaling, so endocrine therapy is not the primary effective treatment for them.