The objective of our study is to evaluate whether vitamin D3 conjugated to gold nanoparticles—VD3-GNPs—can reduce breast cancer aggressiveness and alter important cancer cellular pathway proteins (PI3K/AKT/mTOR, ETV7, and YAP/TAZ), so that the VD3-GNPs can be a cancer therapy. The gene discussed is YAP1; the disease is cancer.