The MCF7 LTED line provides an in vitro parallel of these clinical Wortmannin mTOR findings because, when Inhibitors,Modulators,Libraries these cells are re exposed to estradiol, cell growth slows dramatically, followed by a period of recovery dur ing which cell growth once again becomes estrogen dependent. To determine whether MCF7 LTED R cells also recovered sensitivity to PI3K inhibition, the effects of BGT226, BKM120 and RAD001 treatment were com pared between MCF7 LTED R cells and MCF7 LTED cells. Consistent with partial recovery of sensitivity to PI3K inhibition, lower doses of BGT226 were able to induce apoptosis in estrogen deprived MCF7 LTED R cells in comparison with MCF7 LTED cells. In contrast, the levels of cell death with BKM120 were similar Inhibitors,Modulators,Libraries in all three MCF7 cell line variants and sensitivity to RAD001 was lost in MCF7 LTED R cells despite reintroduction of estrogen deprivation.

PIK3CA mutations are common in relapsed ER positive breast cancer The in vitro studies described above suggested that a combination of fulvestrant and a PI3K pathway inhibitor may be an effective approach for aromatase inhibitor resistant advanced breast cancer, particularly in PI3KCA mutant cases that are persistently ER positive at relapse. Inhibitors,Modulators,Libraries Since PIK3CA mutation has been reported to be asso ciated with a more favorable prognosis, however, it was unclear how many patients with ER positive PIK3CA mutant breast cancer would present with advanced disease. Fresh frozen research biopsies were therefore obtained from 51 patients with recurrent or metastatic disease for PIK3CA mutation testing. Their median age at initial cancer diagnosis was 53.

4 years. The median follow up was Inhibitors,Modulators,Libraries 51. 7 months. Forty three out of the 51 patients were deceased at the time of analy sis. At initial diagnosis, 32 Inhibitors,Modulators,Libraries tumors were ER positive, 17 tumors were ER negative, and two tumors were of unknown status. Five out of the 32 ER positive tumors changed to ER negative status at recurrence. PIK3CA mutation analysis was performed on the 27 ER positive and 24 ER negative recurrent specimens. We included both ER positive and ER negative cases to interrogate the relationship between PIK3CA mutation and ER status in the recurrent disease population. A PIK3CA mutation was identified in 16 of the 51 tumors, a prevalence similar to that observed in studies that examined primary breast cancer tissue. PIK3CA mutation was strongly associated with ER posi tivity.

Among the 27 ER positive tumors, 13 were PIK3CA mutant. In contrast, only three of the 24 ER negative EPZ-5676 DOT1L tumors were PIK3CA mutant. ER expression was maintained in 13 out of 14 cases with PIK3CA mutation. Consistent with previous reports, PIK3CA mutation was associated with a later relapse pattern, with a trend for patients with PIK3CA mutant disease exhibiting a lower mortality rate.