The Truth... What is it?

Serum or plasma testing for CA27.29


See the file on our pathology group's website. This agent is one of several serum "tumor marker" antigens which can be detected in a patient's blood. Different test systems or test manufacturer's may lead to different names for the same (or nearly the same) test...the "name" tending to indicate the specific antibody. CA27.29 is a one-epitope antibody (automated testing on the Chiron ACS system) generated against a particular antigen epitope on a mucinous protein in the MUC1 family (there are 6-7 MUC families). This test is a breast cancer test, and it is best used as a serial test wherein doctors are looking for increase or decreases from whatever the level was at the starting point. It is essential for patients to keep in mind that the "normal range" for most lab tests is + or - 2 standard deviations from the "mean" of values found in a group of normal people (rule of thumb: "normal" includes about the 85% of normals closest to the mean).


  • monitor breast cancer treatment...see if high levels drop with treatment.
  • monitor for recurrence from a state of cure/remission...see if levels start rising.
  • as a clue to the origin of a cancer "of unknown primary"...high levels mean "look for breast".

Causes of DECREASED Values/Levels

  • normal range is down to zero
  • one hopes to see decreases during cancer treatment


Causes of INCREASED Values/Levels

  • high breast cancer-caused elevations: value tends to correlate with tumor burden
  • about 2% of normals run a mildly elevated value (less so with CA27.29 than CA 15-3)
  • rare (3 of 253 cases) patients develop an elevation which remains steady...a test-system artifact/discordance (can't be confirmed by Western Blot test)
  • breast cancer recurrence elevations more likely with mets to lung, liver, or bone (so, in general, test is 77% good that an elevation means a recurrence has taken place).
  • may not elevate early with breast cancer recurrence elsewhere (so, in general, test is 90% good that a "normal value" means no recurrence)
  • cysts of ovary (even common follicular cysts)
  • cases with uterine fibroids (leiomyomata)
  • intestinal/colonic problems: from irritable bowel syndrome, to enteritis, to colitis.
  • medications: Paxil
  • chronic hepatitis and/or cirrhosis of the liver
  • sarcoidosis
  • tuberculosis
  • systemic lupus erythematosus (SLE)

Other names for this exact or approximate agent are: breast carcinoma associated antigen; MAM6; milk mucin antigen; CA 15-3 (a two-epitope test automated on the Abbott IMx system); MCA; CA549; CA M26; and CA M29. CA27.29 antigen is detected by an antibody to an epitope in the protein core of this MUC1 protein. Reference:

  • Clinical Chemistry, May 1999, page 630


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(initially posted: 23 Dec. 2000)