The isolation and culture of tumour cells from both neu and neu/S100A4 transgenic mice increased the efficiency of mammary tumour production from 44 and 68% as seen after 14 months in neu and neu/S100A4 transgenic mice (Davies et al, 1996), respectively, to 100% in the nude mice for all of the injected cell lines. The gene discussed is S100A4; the disease is breast cancer.