The cancer antigen 15-3 (CA 15-3) biomarker test is used to monitorbreast cancerand its response to treatment.
Purpose
CA 15-3 is an antigen that’s normally found in breast tissue.
Antigens are proteins that identify a cell, acting as its “signature.”
Verywell / Theresa Chiechi
While the CA 15-3 antigen does not cause cancer, the level can increase as cancer cells multiply.
The number of CA 15-3 antigens will increase with a tumor’s growth.
That said, not all breast cancers produce CA 15-3 antigens.
This is especially true with early-stage breast cancer.
The CA 15-3 test also has low sensitivity because breast cancer doesn’t always cause it to increase.
Routinemammogramsare considered the frontline tool for breast cancer screening in most countries.
Risks and Contraindications
There are few risks associated with the CA 15-3 test.
The test requires a blood draw, which may cause mild pain, redness, or bruising.
Light-headedness and fainting may also occur.
Less commonly, the blood draw may cause ahematoma, which is an accumulation of blood under the skin.
Most small hematomas go away on their own; larger ones may require treatment.
Infection is rare following a blood draw if standard health precautions are taken.
There are no preparations needed for any of these tests.
Timing
The blood draw takes only a few minutes.
Depending on the registration and the waiting time, your appointment can take 3090 minutes.
Location
The CA 15-3 test can often be performed at the oncologist’s office during your visit.
Otherwise, you may be referred to a nearby lab.
Food and Drink
There are no food or drink restrictions for the CA 15-3 test.
Doing so won’t affect the results, but may plump your veins and make the blood draw easier.
Medications That Alter Results
Certain medications and supplements can interfere with the CA 15-3 test.
Stop taking any supplement containing more than 0.03 milligrams of biotin 72 hours before the test.
In addition, the targeted cancer drug Afinitor (everolimus) may cause paradoxical effects.
You should tell thephlebotomistif you are on Afinitor so a notation can be made for the reviewingpathologist.
Check your policy or call your health insurer for details.
Find out which form of payment the office accepts before you go to your appointment.
Many labs will ask you to pay yourcoinsurance or co-paycosts in advance; others will bill you later.
A consent form may also be provided.
The blood draw, also known venipuncture, is performed by a phlebotomist.
You may be asked to pump your fist several times if your veins are small.
The site is then swabbed with an alcohol pad.
You will feel a small prick as the needle is inserted.
For the CA 15-3 test, the phlebotomist will need to obtain a minimum of 0.3 milliliters of blood.
The vacuum-sealed test tube will usually have a red top or a gel barrier.
The phlebotomist then applies an adhesive bandage over the puncture wound.
you’re able to then continue your day as usual.
After the Test
You may feel sore or develop redness or bruising at the puncture site.
These issues will usually resolve on their own without treatment.
If needed, you’re able to take Tylenol (acetaminophen) to help alleviate the pain.
Do not apply ice directly to the skin or leave it on for longer.
The report will include a reference range outlining the normal and abnormal CA 15-3 levels.
Sometimes CA 15-3 levels can be abnormally elevated during the first four to six weeks of new cancer therapy.
Any treatment that disrupts a tumor can cause a temporary rise in tumor markers.
It is only when levels rise that further investigation may be warranted.
If your CA 15-3 results are elevated, your oncologist will likely order additional tests.
If elevation persists or increases, your healthcare provider may order additional testing.
Results should be examined in the context of your health and other diagnostic evaluations.
Having a temporary increase in CA 15-3 levels does not necessarily mean that your cancer is spreading.
Along those same lines, a temporary decrease does not necessarily mean that the cancer is disappearing.
Non-cancer-related explanations can include endometriosis, pelvic inflammatory disease, chronic hepatitis, and more.
Your doctor will do more tests to explore the underlying cause of the elevated marker.
A CA 15-3 measure that’s less than 30 units per milliliter (U/mL) is considered normal.
Both of these test for cancer antigens.
However, CA 27.29 and CA 15-3 measure different tumor markers.
While their results are often related, they are different and should not be used interchangeably.
Doctors can use them as one piece of information among many.
Your doctor will be able to provide you with more information based on other tests they do.
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