Prognostic impact of progesterone receptor expression in HER2-negative luminal B breast cancer

Abstract

Aim: The new classification of breast cancer is based on microarray studies. Within the estrogen receptor (ER) positive breast carcinoma subtype further subgroups could be identified. In the present study, we analyzed the Her2 negative, highly proliferative subgroup (Luminal B1-like, LUMB1) with emphasis on their clinicopathological characteristics and progesterone receptor (PR) expression.

Patients and methods: Our retrospective study concerned the period between 2000 and 2010. 158 patients were selected with ER positive, Her2 negative, Ki67>15% breast cancer. The pathological and clinical data were collected and analyzed. Age, tumor grade and stage, ER, PR, Her2 and Ki67 expression were recorded. The clinicopathological variables were correlated to PR expression.

Results: The mean age of the patients was 57.5 (28-75) years. The ratio of patients younger than 40, was 8.86%. Shorter metastasis-free survival was observed in this young age group (P=0.044). The majority of our cases belonged to the pT1-pT2 stages (41.28% and 44.95%, respectively) whereas pT3 and T4 stage was detected in 5.50% and 8.25% of the cases, respectively. Almost half of the cases had no axillary lymph node metastasis (pN0: 48.91%), 1-3 lymph node metastases were detected in 38.04% (pN1), 4-10 metastatic lymph nodes were identified in 9.78% (pN2) and pN3 stage was found in 3.26% of the cases. Most commonly the tumors were either grade 2 or 3 (44.16% and 45%, respectively). The median value of Ki67 labeling index was 30%. Disease progression was detected in 36.19% of the patients. According to PR expression, a tendency to better prognosis (i.e. longer disease free- and overall survival) was detected in cases showing >10% PR positivity. However, no difference was found regarding tumor size, axillary stage, grade and age when comparing lower and higher PR expressing tumors.

Conclusions: LUMB1 breast carcinomas are typically grade 2 and grade 3, the Ki67 labeling index is often 30% or higher. Distant metastases occur in more than one third of the cases. Within this subgroup, those cases with low PR expression represent a poor prognostic cohort. These findings require further investigations in larger number of LUMB1 breast cancer cases.