CHANGES IN MESSENGER-RNA EXPRESSION OF PROTEIN-KINASE-A REGULATORY SUBUNIT I-ALPHA IN BREAST-CANCER PATIENTS TREATED WITH TAMOXIFEN

RNA for protein kinase A regulatory subunit I alpha (RI alpha) has bee n measured in tumors from 32 breast cancer patients before and during primary treatment with tamoxifen. Values in pretreatment specimens wer e significantly higher in tumors subsequently responding to treatment as compared with those not (P = 0.004 by Mann-Whitney U test). Further more, whereas levels fell with treatment in 16 of the 24 responding tu mors, they did not in any of the 8 tamoxifen-resistant tumors (and ind eed rose in 6 cases). These results suggest that measurement of RI alp ha mRNA may help in identifying endocrine-dependent breast cancers and provide further evidence of the involvement of the protein kinase A s ystem in response and resistance to tamoxifen treatment.