The ratio of progesterone receptor isoform A to B determines the effect of antiprogestins on preclinical models of breast cancer metastasis

ÁLVAREZ, MICHELLE MARILYN; GIULIANELLI, SEBASTIÁN; RIGGIO, MARINA; SEQUEIRA, GONZALO; MAY, MARÍA; NOVARO, VIRGINIA; SAHORES, ANA; LAMB, CAROLINE A.; LANARI, CLAUDIA

San Antonio

Congreso; San Antonio Breast Cancer Symposium; 2015

In previous studies using several experimental models expressing different progesterone receptor (PR) isoform ratios, wehave shown that only those with high levels of isoform A (PRA) are inhibited by antiprogestins whereas those with high levels ofisoform B (PRB) are resistant to antiprogestin therapy. Moreover, results obtained using tissue cultures of breast cancer patientsconfirmed the data observed in these experimental models (May and Rojas et al., ASCO meeting 2015).The aim of this study was to evaluate the role of progestins and antiprogestins on the outgrowth of spontaneous metastatic foci ofmammary carcinomas with different PR isoform ratios.We used metastatic tumors from the murine medroxyprogesterone acetate (MPA)-induced breast cancer model: C7-2-HI(PRA>PRB) and C7-HI (PRA