Abstract P6-06-29: Single progesterone receptor positive (PgR+) is a predictive marker for endocrine therapy but not a prognostic factor in ER-/PgR+/HER2- breast cancers

Abstract

Background: Single hormone receptor positive, especially single progesterone receptor positive (PgR+), although uncommon, is a unneglectable phenomenon given the large patient population. There is dispute as to single PgR positive is truly positive since PgR is a downstream molecule of estrogen receptor and when HER2 is negative at the same time, it is puzzling whether ER-/PgR+/HER2- breast cancer resemble triple negative breast cancer (TNBC) biologically and clinically. However, little is known about that. Therefore, we explore the role of single PgR positive by comparing ER-/PgR+/HER2- breast cancers with TNBCs. Methods: Among 3966 early breast cancer patients operated consecutively in Cancer Hospital, Chinese Academy of Medical Sciences from Jan 2005 to May 2008, 240 (6%) cases were identified as ER-/PgR+/Her2-and 348 (8.7%) cases as TNBCs. Clinicopathological characteristics and survival were analyzed respectively and then compared between 2 subtypes. Results: The average age of diagnosis was 49 yrs in both groups. For ER-/PgR+/HER2- patients, 213(88.8%) patients received adjuvant chemotherapy and 183 (76.3%) patients got adjuvant endocrine therapy. Axillary lymph node involvement was independent poor prognostic factor for Relapse-free survival (RFS) and overall survival (OS) (RFS: HR 1.728,P = 0.001; OS: HR 2.778, P<0.0001). Patients receiving adjuvant endocrine treatment had better survival than patients receiving no endocrine therapy (RFS: HR 0.594, P = 0.086; OS: HR 0.218,P<0.0001). Similarly, axillary lymph node involvement and large tumor size were found to be the poor prognostic factors for TNBC group. When compared with TNBCs, patients with ER-/PgR+/HER2- tumors tended to have lower tumor grade (P = 0.051) and smaller tumor size (P = 0.036). The metastatic patterns were comparable while RFS and OS demonstrated no difference between ER-/PgR+/HER2- and TNBC patients (5-year RFS rate: 80.7% vs 77.4%, P = 0.330; 5-year OS rate: 88.0% vs 85.2%, P = 0.290). Further analysis showed that ER-/PgR+/HER2- patients receiving adjuvant endocrine treatment had more favorable RFS and OS while ER-/PgR+/HER2- patients without endocrine therapy had worse overall survival compared with TNBC patients. Table 1: 5yr RFS and OS in ER-/PgR+/HER2- patients compared with TNBC patients RFS OS 5-year RFS rateHR(95%CI)P5-year OS rateHR(95%CI)PER-/PR+/HER2- with endocrine therapy (N = 183)84.0%0.686(0.453-1.038)0.07593.0%0.410(0.219-0.768)0.005ER-/PR+/HER2- without endocrine therapy (N = 57)70.1%1.392(0.824-2.353)0.21771.9%2.166(1.252-3.746)0.006TNBC as control(N = 348)77.4% 85.2% Conclusions:This is the largest sample size to date looking at patients with ER-/PgR+/HER2- breast cancers specifically. It shows that without endocrine therapy, this group of patients may have worse outcomes than TNBC patients, indicating that it should be regarded as biologically and clinically distinct group of breast cancer and PgR intrinsically does not play a key role. PgR itself is not a good prognostic factor. However, adjuvant endocrine therapy could benefit this group of patients, suggesting estrogen signaling may still work via different pathways which might involve PgR. Further studies should be done to unravel the underlying mechanism. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P6-06-29.