HMT-3522 S1, also known as HMT-3522/wt, is a subline that has been derived from HMT-3522. The parent line was established from a benign breast tumour of a 48 year old woman and has undergone spontaneous malignant transformation. It was grown on collagen in serum-free media without antibiotics from explantation onwards. A mutation at codon 179 of the p53 gene was detected during establishment of the parent line.HMT-3522 S1 is a continuation of this line from passage 34 and is grown without collagen.It is near-diploid, but an evolution of karyotype has been observed by regular chromosomal analyses. The expression of cytokeratin 13, 14, 17 and 18 and vimentin has been reported. Expression of EGF-R, c-erb-B2, N-myc, c-ras-Ha1, c-ras-Ki2 and N-ras was shown to fluctuate slightly with passage number. The cells have tested negative for estrogen receptor, c-erbA1, c-erb-A2, int-2 or hst-1. During propagation growth factor requirements decreased simultaneously with amplification and overexpression of c-myc protooncogene. In a three-dimensional basement membrane culture assay the phenotypic characteristics of normal breast tissue in vivo are recapitulated. This cell line has remained non-tumorigenic for more than 400 passages. Publications using this cell line must refer to the original paper (Briand et al., In Vitro Cell Dev Biol 1987; 23:181). Any sublines created must include the name HMT-3522 in the designation, but a short name may be used in the same paper.Subline HMT-3522 S2 (ECACC catalogue no. 98102211) has been isolated by culturing S1 cells from passage 118 in serum-free media without epidermal growth factor (EGF). This cell line grows on collagen-treated flasks.The third subline, HMT-3522 T4-2 (ECACC catalogue no. 98102212) was established from S2 at passage 238 and is the only tumorigenic line in nude mice out of the 3 sublines. This cell line grows on collagen-treated flasks.