Dealing with MCF-7 ER-positive breast cancer cells, in 2000, Falzon and Du [33] proposed that “intracrine” and “autocrine/paracrine” pathways could transduce opposite instructions to cells, the former being proliferation-restraining whereas the latter inducing cell growth, thus adding a further level of complexity to the biological responses of cells to PTHrP. This evidence concerns the gene PTHLH and breast cancer.