HYAL1 and breast cancer: Firstly, the mRNA expression level of two major HA-related enzymes, the synthase Has-2 and the hyaluronidase Hyal-1, which have been previously associated with BM formation in BC patients, were examined in three BC cell lines corresponding to two different molecular subtypes, namely MCF-7 (luminal), MDA-MB-231 (TNBC), and MDA-MB-231-BR (brain-seeking TNBC) (Figure 1A,B).