CA15.3 - Breast Cancer Marker

CA15-3 is a tumour marker. It is used to check how breast cancer treatment is working and look for cancer that has come back, or recurred, after treatment. CA15-3 is not measured for early stage breast cancer because the levels of this protein are rarely higher than normal at this stage. The levels are the highest when breast cancer has spread to the bones, the liver or both. If the level of CA15-3 goes down or returns to normal, it may mean that treatment is working. If levels increase over time, it may mean that the cancer is not responding well to treatment, is still growing or is coming back (recurring).

However, the gold standard for breast cancer screening is still a routine mammogram.


The normal ranges: < 39.1 U/mL
*Normal value ranges may vary slightly among different labs. Some labs use different measurements or may test different specimens. Talk to your provider about your test results.