Quercetin facilitates growth suppression, apoptosis, and chemosensitivity while inhibiting self-renewal ability, stemness, angiogenesis, metastasis, migration, invasion, proliferation, and EMT of PC cells, which are coordinated through the modulation of EGFR, RAGE/PI3K/Akt/mTOR, NF-κB, ALDH1, EGFR, IL-6, STAT3, SHH, TGF-beta1, Smad2/3, Snail, and p-glycoprotein cascades [198–204]. The gene discussed is PIK3CA; the disease is pachyonychia congenita.