D7 Tumor and oncological markers

Topic

Tumor markers are molecules produced by tumor cells or by the body in response to a tumor, and they can be measured in the blood. In general, they lack sufficient sensitivity and specificity to be used in isolation as a screening tool for cancer in asymptomatic populations, although some have specific applications. Their greatest utility lies in monitoring already diagnosed tumors, evaluating treatment response, detecting early recurrence, and estimating prognosis.

Prostate marker levels can rise due to cancer, but also due to prostate volume, inflammation, and other benign conditions; therefore, an elevated concentration does not, by itself, prove the presence of a tumor. In the 4–10 ng/mL range, refined measurements—such as the free-circulating fraction and the rate of increase—are used. According to the text, a free fraction of less than 15% or an increase of more than 0.75 ng/mL per year is associated with a higher risk of cancer. After complete removal of the prostate, the marker should become virtually undetectable. Its reappearance indicates the persistence or recurrence of tumor tissue and allows for the detection of biochemical recurrence before it necessarily becomes visible on imaging studies.

Carcinoembryonic antigen is primarily used to monitor colorectal or lung cancer. Following tumor removal, a drop to normal levels over the subsequent weeks suggests that the resection was complete. If levels rise again later, this can signal the clinical or radiological onset of recurrence months in advance.

The ovarian marker serves a similar function in monitoring ovarian cancer. A decrease during chemotherapy allows for the assessment of treatment response: the text considers a reduction of at least 50% from the baseline value by the third month to be a favorable outcome. The rate of decline also holds prognostic value, as a more rapid drop is associated with a more favorable course of the disease.

Alpha-fetoprotein has a different application. According to the text, in a patient with cirrhosis, a concentration exceeding 400 ng/mL accompanied by compatible liver imaging findings may allow for the diagnosis of primary liver cancer without the need for biopsy confirmation.

Lactate dehydrogenase (LDH) also does not serve as a specific marker for any particular tumor. It reflects aspects related to metabolic activity and cell necrosis; consequently, levels may rise in various types of neoplasms. Precisely because of this lack of specificity, it can provide prognostic information in diseases such as lymphomas, leukemias, myeloma, and advanced melanoma. In the case of melanoma, a significant elevation is associated with a poorer prognosis. LDH levels can also rise in tumor lysis syndrome, a condition in which the rapid destruction of numerous cells releases their contents into the bloodstream.

The true utility of any marker also depends on the pre-test probability that the patient has the disease. Based on Bayesian reasoning, even a marker with high sensitivity and specificity will yield many false positives when used in a population where the cancer in question is very rare. The text illustrates that a test with 80% sensitivity and 95% specificity would have a positive predictive value of only about 14% if the disease were present in 1% of the population, whereas this figure would rise to approximately 76% if the prevalence were 20%.

This dependence on pre-test probability explains why tumor markers are generally far more useful in patients with a confirmed cancer diagnosis than as general screening tools. In the context of follow-up, a change in marker levels occurs against a backdrop where the likelihood of persistent or recurrent tumor disease is already considerably higher.

Overall, the prostate marker and its refined versions assist in the assessment and monitoring of prostatic disease; carcinoembryonic antigen and the ovarian marker allow for monitoring therapeutic response and anticipating recurrence; Alpha-fetoprotein can aid in the diagnosis of liver cancer in certain contexts, while LDH provides metabolic and prognostic information regarding various neoplasms. When interpreted in light of their temporal evolution and the pre-test probability of disease, these markers serve primarily as tools for monitoring known cancer, assessing treatment response, detecting early recurrence, and estimating disease progression.

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