We next quantified the cellular amounts of miR-21, miR-221 and miR-155, which have previously been reported to be involved in tumor growth, progression and metastasis, in several well-established breast cancer cell lines; they included HCC1954 (ER-, PR-, HER2+), MDA-MB-231, MDA-MB-436 (both triple-negative), MDA-MB-361 (ER+, PRweak, HER2+) and MCF-7 (ER+, PR+, HER2-) (25) as well as pre-cancerous MCF-10A cells (Figure S2). Here, ERBB2 is linked to breast cancer.