In addition, experiments with clonal cell lines isolated from the parental 8701-BC line and endowed with different proliferative and invasive properties in vitro demonstrated the heterogeneity of the growth and invasive response of the different subpopulations to administration of PTHrP fragments, thereby suggesting the existence of complex PTHrP-breast cancer cell interplays in the affected tissue [17]. This evidence concerns the gene PTHLH and breast cancer.