**Core Concept**
Tumor markers are substances produced by cancer cells or in response to cancer. They are used in the management of cancer for diagnostic, prognostic, and therapeutic purposes. Tumor markers can be used to identify cancer early, monitor the response to treatment, and detect recurrence.

**Why the Correct Answer is Right**
Tumor markers are used for various purposes in cancer management. Option b) Follow up of a cancer patient, especially for knowing about recurrence is a key use of tumor markers. This is because tumor markers can be elevated in response to cancer recurrence, allowing for early detection and intervention. For example, the tumor marker CA-125 is used to monitor ovarian cancer recurrence. Other tumor markers, such as PSA, are used to monitor prostate cancer recurrence. Additionally, tumor markers can be used to monitor the response to treatment and adjust the treatment plan accordingly.

**Why Each Wrong Option is Incorrect**
**Option A:** Screening of a cancer - While some tumor markers can be used as screening tools, they are not the primary method of screening for cancer. Other methods, such as imaging studies and physical exams, are more commonly used for cancer screening.
**Option C:** Confirmation of a diagnosed cancer - Tumor markers are not used to confirm a diagnosis of cancer. A diagnosis is typically made through a combination of clinical evaluation, imaging studies, and biopsy results.
**Option D:** For monitoring the treatment of a cancer - While tumor markers can be used to monitor the response to treatment, this is not their primary use. Monitoring the response to treatment is typically done through a combination of clinical evaluation and imaging studies.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that tumor markers are not specific to cancer and can be elevated in response to other conditions, such as inflammation or pregnancy. Therefore, a positive tumor marker result should be interpreted in the context of the patient's clinical presentation and other diagnostic findings.

**Correct Answer:** B. Follow up of a cancer patient, especially for knowing about recurrence