ERBB2 and breast cancer: Hence, the main four subtypes of BC are luminal A (ER+, PR+, and HER2−), luminal B (ER+, PR− or PR+, and HER2−), HER2 positive (ER− or ER+, PR− or PR+, and HER2+), and triple negative (ER−, PR−, and HER2−) [34].