Ectopic production of
placental proteins by a variety of nontrophoblastic epithelial
tumors is well recognized.
Pregnancy-specific beta-1 glycoprotein (SP-1), a recently described placental
protein, has been detected both in the serum and
tumors of patients with
breast carcinoma. To assess the significance of SP-1 in
breast carcinoma, we stained 139 cases of primary
breast carcinoma for SP-1 using the immunoperoxidase technique. Overall, 55 (40%) of breast
cancers were positive for SP-1; focal positivity was also noted in normal breast epithelium and fibrocystic disease. Both intraductal (32%) and infiltrating duct (43%)
carcinomas were more often positive than either in situ (5%) or infiltrating (26%)
lobular carcinomas. SP-1 positivity in
tumors of infiltrating duct morphology less than 3 cm in diameter, correlated highly (P less than 0.01) with the presence of axillary
lymph node metastases. The presence of SP-1 in normal breast epithelium and fibrocystic disease and the low rate of positivity in
lobular carcinoma casts doubt on the usefulness of SP-1 as a
tumor marker. However, these findings suggest that immunopositivity for SP-1 in small infiltrating duct
carcinomas may be an
indicator of poor prognosis.