Clinical assays for tumor markers are most important for:

• A. Screening for the presence of cancer
• B. Monitoring the course of a known cancer
• C. Confirming the absence of disease
• D. Identifying patients at risk for cancer

Answer: (B)

The main idea is that tumor markers are most useful for tracking disease activity in people who already have a known cancer. By measuring the marker over time, clinicians can see how the tumor is responding to therapy, whether the disease is stable, progressing, or returning after treatment. This serial information helps guide treatment decisions and early detection of relapse.

These markers aren’t reliable for screening asymptomatic individuals because they often lack enough sensitivity and specificity; many noncancer conditions can raise the marker, and not all cancers produce a marker at detectable levels. They also cannot definitively prove that all disease has been eradicated, since micrometastases or marker fluctuations can occur despite treatment. Identifying people at risk for cancer relies on risk factors, genetics, imaging, and population-based data rather than tumor marker assays.

So, the strongest role of tumor markers is to monitor the course of a known cancer. For example, serial monitoring of markers like PSA in prostate cancer or CA-125 in ovarian cancer helps assess response to treatment and detect relapse.