Progesterone receptor loss identifies Luminal B breast cancer subgroups at higher risk of relapse

BACKGROUND: The immunohistochemical (IHC) evaluation of estrogen receptor (ER), progesterone receptor (PgR), Ki-67 and HER2 is considered a surrogate means for identifying the molecular subtypes of breast cancer with different prognosis. PATIENTS AND METHODS: We explored patterns of recurrence in 4837 women with breast cancer defined as Luminal B (ER-positive and/or PgR-positive, HER2 positive and/or Ki-67≥14%) by IHC classification. We evaluated four subgroups within the Luminal B subtype according to HER2 expression and PgR status. RESULTS: Patients within the ER+/PgR+/HER2- subgroup presented a 5-year breast cancer-related survival (BCS) of 97% (95% confidence interval (CI), 96-97) and overall survival (OS) of 95% [95% CI, 95-96], the best survivals of the Luminal B subgroups. In the multivariate analysis, the ER+/PgR-/HER2- subgroup was associated with a reduced BCS (HR 1.71; 95%CI, 1.25-2.35) and OS (HR 1.47; 95%CI, 1.10-1.96) when compared with the ER+/PgR+/HER2- subgroup. Also patients within the ER+/PgR-/HER2+ subgroup had a reduced BCS (HR 1.93; 95%CI, 1.32-2.83) and OS (HR 1.62; 95%CI, 1.14-2.30) when compared with ER+/PgR+/HER2- subgroup. On the other hand, no statistically significant differences were found with regard to BCS and OS among patients with ER+/PgR+/HER2+ and patients with ER+/PgR+/HER2- disease. CONCLUSIONS: PgR loss identifies Luminal B breast cancer subgroups at higher risk of relapse and death, both with HER-2-positive and HER-2-negative disease.