Müller et al. [158] using quantitative PCR, found that HPRT was detectable in cultured human MDA-MB-231 breast carcinoma cells, primary tumors, and tumor-infiltrated lungs of SCID-mice injected with human MDA-MB-231 breast carcinoma cells, but undetectable in normal mouse lungs, and that the human HPRT mRNA content in lungs of mice correlated with the size of the tumor. Here, HPRT1 is linked to breast carcinoma.