If a tumor marker rises after chemotherapy, which interpretation is most likely?

• A. Effective therapy
• B. Progression or nonresponse
• C. Measurement error
• D. Remission

Answer: (B)

Tumor markers reflect how much tumor activity is present. When chemotherapy is effective, the tumor burden decreases and the marker levels tend to fall as the cancer shrinks. If the marker rises after starting treatment, the most likely interpretation is that the disease is progressing or not responding to therapy, meaning the tumor is continuing to grow or survive despite treatment. This rise should prompt re-evaluation with imaging and clinical assessment to confirm progression. While occasional short-lived increases can happen from tumor cell click-through release or assay variability, a persistent rise over time is the stronger signal of progression rather than remission or a successful response.