HMT-3522 T4-2, also known as HMT-3522/mt-1, is a subline that has been derived from HMT-3522. The parent line was established from a benign breast tumor 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 at passage 25-30