A selection of PDXs (ER− PR− HER2−, ER+, PR+ HER2−, ER+ PR− HER2− and ER− PR− HER2−) that have never been cultured in vitro but have been propagated in NOD/SCIDy mice were used to increase the likelihood of tumour take (Table 1) [18]. This evidence concerns the gene PGR and neoplasm.