ERBB2 and breast cancer: The molecular classification of breast cancer divides mammary carcinomas into hormone-dependent tumors (Luminal A, Luminal B and tumors with overexpression of the HER-2 oncogene) and hormone-independent, such as triple-negative tumors like MDA-MB-231, which do not express ER, PR or HER2, leading to a higher risk of recurrence and worse prognosis [4].