Differential patterns of recurrence and specific survival between luminal A and luminal B breast cancer according to recent changes in the 2013 St Gallen immunohistochemical classification.

INTRODUCTION: In 2011, the St Gallen panel introduced several changes in breast cancer classification, thereby creating the luminal B Her2- subtype. In 2013, the panel also included Ki67 overexpression and PR <20 % as risk factors, while excluding GH3 in the absence of increased Ki67. We compared the classification of 2011 modified with the new 2013 St Gallen classification. PATIENTS AND
METHOD: Consecutive breast cancer patients referred to the Breast Unit of the University Hospital Mútua Terrassa and Hospital of Terrassa for surgical treatment of either primary or recurrent tumors were prospectively included between 1997 and 2014. Eventually, 1,874 cases were included for the four-subtype analysis. The median follow-up was of 66 months.
RESULTS: Using the 2013 St Gallen classification no significant differences were found in specific mortality rates between luminal A and B subtypes. There were significant differences at 5, 10, and, 15 years if we excluded luminal A GH3 patients in the absence of increased Ki67 (p = 0.004, 0.005, and 0.007). Luminal A sub-type patients showed significantly less distant metastases than the rest, including luminal B Her2- patients (p < 0.001). Also, luminal B patients showed significantly less distant metastases than pure Her2 (0.05) and triple negative (TN) (p < 0.001). There were no differences between pure Her2 and TN patients (0.055), neither among the different luminal B sub-types.
CONCLUSION: GH3, PR, and Ki67 may all be discriminatory factors for metastasis and specific mortality. Therefore, we suggest including GH3 in the luminal B subtype in the absence of Ki67.