This is proportional to the proportion of OCs among healthy cells (pOC=ρOCρOC+ρOB) and lack of bone 1 − B. In the second summand, δ is the benefit that an OB receives from interacting with any PCa cell as the PCa cells secrete modest amounts of TGF-β. This evidence concerns the gene TGFB1 and posterior cortical atrophy.