Which of the following biomarkers is not typically associated with breast cancer?

The correct choice in this question is associated with alpha-fetoprotein (AFP), which is not typically linked to breast cancer. AFP is primarily a biomarker used in the diagnosis and monitoring of liver cancer and germ cell tumors. In contrast, the other biomarkers listed—HER-2, PR (progesterone receptor), and ER (estrogen receptor)—are commonly associated with breast cancer.

HER-2 refers to a protein that can promote the growth of cancer cells, and its overexpression is a significant factor in a subtype of breast cancer. PR and ER are hormone receptors that indicate how well breast cancer cells respond to hormone therapy, which plays a crucial role in managing certain breast cancer types. Therefore, while HER-2, PR, and ER are integral to breast cancer characterization and treatment strategies, AFP does not have a recognized role in breast cancer, reinforcing its identification as the outlier in this context.