Cancer Antigen 27.29 (CA 27.29) is a protein often found in higher levels in the blood of individuals with certain types of cancer, most notably breast cancer. It is used primarily as a tumor marker to monitor the progression of breast cancer and the effectiveness of treatment.
CA 27.29 is a fragment of the MUC1 protein, a mucin glycoprotein released into the bloodstream by breast cancer cells. Clinically, CA 27.29 levels are measured to monitor the effectiveness of treatment for breast cancer. Decreasing levels typically indicate the treatment is working, while increasing levels may suggest disease progression or recurrence. After initial treatment, regular monitoring of CA 27.29 can help detect early recurrence of breast cancer.
The antigen is measured through a blood test, often assessed alongside other markers such as Cancer Antigen 15-3 (CA 15-3) to provide a more comprehensive picture. Typically, CA 27.29 levels less than 40 U/mL are considered normal. Elevated levels may indicate the presence of breast cancer or other conditions such as liver disease or benign breast disease. It is not specific to cancer and must be interpreted in the context of other clinical findings and diagnostic tests.
One limitation of CA 27.29 is its lack of specificity; elevated levels can occur in non-cancerous conditions, leading to false positives. Due to this lack of specificity, CA 27.29 is not recommended for cancer screening in asymptomatic individuals. Other tumor markers used in breast cancer include CA 15-3 and carcinoembryonic antigen (CEA), which can sometimes be used in conjunction to improve diagnostic accuracy.
In patients with known metastases, a reduction in levels of CA 27.29 indicates an excellent response to treatment. In contrast, increasing levels indicate resistance to therapy and progressive disease and justify further clinical evaluation and regular monitoring. It has also been shown that an elevation of CA 27.29 levels above the upper limit of normal in patients with no clinical evidence of disease is an early indicator of recurrence. An elevated serum CA 27.29 level in patients in remission of stage II or III breast cancer provided a positive predictive value of 83% for recurrent disease, with an average lead time of 5 months before recurrence was clinically established.
While CA 27.29 is a valuable biomarker in managing breast cancer, particularly for monitoring treatment response and detecting recurrence, its interpretation requires careful consideration of other clinical and diagnostic information.
