In 2009, the American Cancer Society estimated that 192,370 new cases of breast cancer would be diagnosed in the year. A number of pathological factors, including tumor size, the spreading of the tumor and how quickly the tumor is growing, help determine treatment and prognosis. Biological markers can also assist in deciding the most effective treatment and help monitor for breast cancer recurrences.
What is a Tumor Marker?
Tumor markers in breast cancer are either found in the serum of the patient or on the cancer itself. Tumor markers can be produced only by cancer cells or produced because of the body's response to the cancer. Some markers are produced by all cells and it is the increase in cell numbers because of the tumor that causes an abnormal expression. Most tumor markers are proteins, and some are specialized proteins such as receptors found on the cell surface, which bind other proteins. Tumor markers are often used with other clinical symptoms, examination and patient history to determine diagnosis, treatment and any recurrence.
Markers Used in Breast Cancer
Some markers help determine which treatment will be effective and some markers are prognostic, which means they determine the likely outcome of the cancer. Other markers determine the tumor's probable response to treatment. HER-2 is a special protein on the surface of cells that is both prognostic and determines the treatment that should be pursued. Though not true tumor markers, the estrogen receptor and the progesterone receptor determine, like HER-2, which treatment should be administered. CA 15-3 is produced by normal breast cells and an increase in cell numbers will result in elevated levels. However, increases in this marker can also be caused by other non-cancerous conditions. Other markers in breast cancer include those that identify dividing cells such as Ki67, those involved in cell movement such as uPA and PAI-1, and others found in the developing fetus and cancer cells such as CEA.
Diagnosing Breast Cancer
Tumor markers are not generally used to detect breast cancer because they are not yet specific enough. The markers CA 15-3 and CA 27-29 are found in patients with breast cancer. However, they are also linked with other cancers and benign conditions such as liver disease and pregnancy.
Tumor Markers and Prognosis
The pathology of the breast cancer, such as size and whether it has spread to the lymph nodes, are all markers of prognosis. However, a number of tumor markers have also been shown to be linked with prognosis in breast cancer. Professor Joe Duffy and colleagues from St. Vincent's Hospital Ireland, published in the journal Clinical Cancer, showed that high-levels of CA 15-3, even in patients with clear lymph nodes, showed a worse prognosis. High concentrations of the marker HER-2 have also been shown to indicate a lower disease free interval and reduced survival time.
Tumor Markers and Treatment
Tumor markers can determine which treatments should be used. For example, HER-2 positive breast cancers respond to Herceptin, while other breast cancers that are estrogen receptor positive will respond to drugs such as tamoxifen. Tumor markers might also determine whether the treatment is making the tumor smaller. Dr. Linbo Wang and colleagues from Zhejang University College China published a study in the journal BioMed Central Cancer in 2009 that indicates the estrogen receptor could predict the tumor's response to a number of chemotherapy treatments.
Tumor Markers and Follow-Up
A study by Dr. Andrea Nicolini and colleagues from the University of Pisa Italy published in the journal Biomedicine and Pharmacotherapy in 2003, compared the follow-up of mastectomy patients by comparing conventional methods to monitoring levels of tumor markers. Patients whose tumor marker or markers increased commenced treatment before the recurrence was identified by conventional methods showed a prolonged disease-free and overall survival rate comparable to those monitored only with conventional methods.
Clinical Use of Tumor Markers
The American Society of Clinical Oncology reviewed its recommendations in the use of tumor markers in 2001. It did not support the use of tumor markers for screening, diagnosis, staging or routine surveillance. However, it did recommend the use of estrogen and progesterone receptors and HER-2 on diagnosis or recurrence because these markers can help decide on the appropriate treatment.
References
- American Cancer Society: What are the Key Statistics for Breast Cancer?
- PubMed.gov: Cancer Study
- PubMed.gov: The Potential Biomarkers in Predicting Pathologic Response of Breast Cancer
- PubMed.gov: "Tumour Marker Guided" Salvage Treatment Prolongs Survival
- PubMed.gov: 2000 Update of Recommenations for the Use of Tumor Markers in Breast and Colorectal Cancer
