Which tumor marker is commonly used to determine whether specific targeted therapy is appropriate for colorectal cancer?

The KRAS mutation is a key tumor marker used to determine the appropriateness of targeted therapies for colorectal cancer, particularly in cases of metastatic disease. The presence or absence of specific KRAS mutations can guide oncologists in selecting appropriate treatment options, especially when considering anti-EGFR (epidermal growth factor receptor) therapies. If a patient has a KRAS mutation, they typically will not benefit from EGFR inhibitors like cetuximab and panitumumab, as these therapies are not effective in tumors with such mutations.

In contrast, other tumor markers listed do not serve the same role for colorectal cancer. Alpha-fetoprotein (AFP) is primarily used in liver cancer and germ cell tumors, while CA-125 is mostly associated with ovarian cancer and does not directly inform treatment decisions in colorectal cancer. The estrogen receptor (ER) and progesterone receptor (PR) are relevant markers in breast cancer, not colorectal cancer, thus further establishing that KRAS testing is the relevant choice in this context.