Abstract P3-04-05: Prognostic effect of semiquantitative measurement of PgR in luminal type breast cancer
Authors: Kim MK , Han W 
Published: May 2016

Background: The identification of prognostic factors for hormone receptor(HR)-positive and human epidermal growth factor receptor 2(HER2)-negative breast cancer is an important issue for the accurate determination of the indications for chemotherapy. The progesterone receptor(PgR) is a downstream molecule induced by transcriptional activation of estrogen signaling. In recent report, quantitatively low PgR expression was significantly associated with a poorer prognosis for patients treated with anastrozole and/or tamoxifen. These findings seem to suggest that the clinically used Ki-67-based IHC classification of luminal subtypes is inaccurate and that semiquantitative measurement of PgR expression can improve the IHC-based classification.

Method: 1327 consecutive patients with ER and/or PgR-positive HER2-negative invasive breast cancer treated with surgery and adjuvant treatment at the Seoul National University Hospital from January 2009 to December 2011 were reviewed. All patients had been pathologically diagnosed with breast cancer, and patients who had received chemotherapy or endocrine therapy before surgery were included. ER, PgR, HER2, and Ki-67 were determined from surgically resected, formalin-fixed, paraffin-embedded tumor tissue. The RFS and OS in Kaplan-Meier plots for the PgR high and low expression groups was compared using the log-rank test. Univariate and multivariate analyses of DFS and OS in relation to various factors were performed with a Cox proportional hazards model, which yielded the HR and 95% of CI for each variable.

Results: Based on pathology data of semiquantitative measurement of the percentage of PgR-positive cells, patients were separated into two groups with PgR percentage cutoff 20%. Among 1372 patients, 665(48.5%) showed high PgR expression, 707(51.5%) showed low PgR expression. PgR expression was relatively high in younger age(&lt;50 years, p&lt;0.001). Higher PgR expression was related to low Ki-67 expression(&lt;10%, p=0.003), and low cancer stage(p&lt;0.001). The DFS and OS of patients in the high PgR subset were significantly better than the low PgR subset only in patients under 50years old.(p=0.005 and 0.037) Cox analysis showed that low PgR expression(HR, 3.06; 95% CI, 1.44-6.47) and negative ER expression(HR, 19.68; 95% CI, 5.89-65.80) were significant independent risk factors for DFS. Low PgR expression(HR, 5.66; 95% CI 1.62-19.74) and high Ki-67 expression(HR 1.06; 95% CI 1.01-1.17) were significant independent risk factors for OS.

Conclusion: We were able to demonstrate that high PgR expression is associated with a better prognosis for luminal type breast cancer. The semiquantitative determination of PgR expression might thus improve the accuracy of the IHC-based classification of luminal A and luminal B breast cancer, especially for premenopausal patients.

Citation Format: Kim MK, Han W. Prognostic effect of semiquantitative measurement of PgR in luminal type breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-04-05.