Big Three startups use immortalized cells for chicken production. Immortalized cells are technically precancerous and divide indefinitely unlike normal cells. Normal animal cells hit Hayflick limit after dozens of divisions. Companies induce immortality via genetic modification or forced mutation. Immortalized cells resemble early-stage cancer cells per MIT biologist Weinberg. Cancer researchers deem eating them impossible to cause human cancer due to species barrier. FDA approved Upside Foods chicken noting even cancerous cells safe after cooking and digestion. No long-term human health studies exist on eating immortalized animal cells. Industry insiders anxious about PR backlash from ''cancer meat'' label. Some startups avoid immortalized cells using slower embryonic stem cells. Believer Meats claims non-cancerous immortalized cells despite skepticism. Upside requires waivers for tasters admitting unknown long-term properties. Cow tumors already enter ground beef supply. Cultured meat raised over $1.2 billion in funding. PETA once offered $1M prize for lab meat. Scale-up plans include massive bioreactors for millions of pounds yearly.