Is SP1 (pregnancy specific beta 1 glycoprotein) elevated in cancer patients?

Pregnancy-specific beta 1-glycoprotein, SP1, was measured in serum by competitive double antibody radioimmunoassay. Very low levels of SP1 or SP1-like activity were found in only 2 out of 85 sera from patients with cancer of the digestive tract, breast cancer, melanoma, and sarcoma, in 2 out of 11 sera from patients with infectious diseases, and in none out of 15 sera from non-pregnant healthy individuals. SP1 thus does not seem to be ectopically produced in vivo by the types of cancer studied, but is probably highly specific for the normal and malignant trophoblast.