Which molecular marker is routinely tested in invasive breast carcinoma to guide targeted therapy?

Which molecular marker is routinely tested in invasive breast carcinoma to guide targeted therapy?

• A. Estrogen receptor and Progesterone receptor
• B. Ki-67 labeling index
• C. BRCA1/2 mutation status
• D. HER2 overexpression

Answer: (D)

The key idea is that some cancer therapies are designed to target a specific molecular feature of the tumor, and the presence of that feature guides treatment choices. In invasive breast cancer, the most important target is the HER2 receptor. When a tumor overexpresses HER2 or has HER2 gene amplification, it predicts a strong and meaningful response to HER2-directed therapies such as trastuzumab and other HER2-targeted agents. Because of this clear predictive value, guidelines require routine testing of HER2 status using immunohistochemistry, with a confirming test if needed, so that patients eligible for these targeted drugs can be identified and treated appropriately. Estrogen and progesterone receptor status is also routinely checked, but it guides endocrine therapy rather than a HER2-directed targeted agent. BRCA1/2 status can influence treatment decisions in certain settings (e.g., use of PARP inhibitors), and Ki-67 is mainly a proliferation marker without a standard targeted therapy that it universally directs. The universal, immediate impact on selecting a targeted drug in most newly diagnosed invasive breast cancers is driven by HER2 status, making it the best answer.

The key idea is that some cancer therapies are designed to target a specific molecular feature of the tumor, and the presence of that feature guides treatment choices. In invasive breast cancer, the most important target is the HER2 receptor. When a tumor overexpresses HER2 or has HER2 gene amplification, it predicts a strong and meaningful response to HER2-directed therapies such as trastuzumab and other HER2-targeted agents. Because of this clear predictive value, guidelines require routine testing of HER2 status using immunohistochemistry, with a confirming test if needed, so that patients eligible for these targeted drugs can be identified and treated appropriately.

Estrogen and progesterone receptor status is also routinely checked, but it guides endocrine therapy rather than a HER2-directed targeted agent. BRCA1/2 status can influence treatment decisions in certain settings (e.g., use of PARP inhibitors), and Ki-67 is mainly a proliferation marker without a standard targeted therapy that it universally directs. The universal, immediate impact on selecting a targeted drug in most newly diagnosed invasive breast cancers is driven by HER2 status, making it the best answer.