Prognostic significance of the progesterone receptor status in Ki67-high and -low Luminal B-like HER2-negative breast cancers.

Background: Breast cancer is a heterogeneous disease, and immunohistochemical evaluation is a surrogate marker that is widely used in clinical settings to identify the intrinsic subtypes. The definition of the Luminal B-like breast cancer was changed at the 2013 St. Gallen meeting; therefore, we investigated the clinicopathological features of the new Luminal B-like breast cancer categorized in the latest definition. We also compared the conventional PgR-high Luminal B-like breast cancer with the conventional PgR-low or -negative Luminal B-like breast cancer.

Patients: We investigated 118 Luminal HER2-negative breast cancer patients who were operated in 2005-2008 at a single institution. Data on each patient's medical history were retrieved.

Results: A subset of patients (14.4 %) was categorized as the new Luminal B-like due to low or negative PgR: 58.8 % were histological grade I, 65 % were T1 in tumor size, and half had node involvement. Chemotherapy was performed in half of the cases. Breast cancer-related events were more frequent for the new Luminal B-like breast cancer than for the Luminal A-like breast cancer and were less frequent than for the conventional Luminal B-like breast cancer. Based on multivariate analysis, low or negative expression of PgR and the absence of hormonal therapy were worse prognostic factors. When categorized into two groups by the PgR status, 48.1 % of the conventional Luminal B-like breast cancer was PgR-high; tumor size was smaller, and nodal involvement was less in this group. The rate of adjuvant chemotherapy of the conventional PgR-high Luminal B-like breast cancer was less than that of the conventional PgR-low or -negative Luminal B-like breast cancer. Breast cancer-related events were significantly lower in the conventional PgR-high Luminal B-like breast cancer.

Conclusions: Our results show the possibility that PgR status has some influence on the prognosis for Luminal HER2-negative breast cancers. Therefore, attention should be paid to the PgR status as well as Ki-67.