Pfizer tanks 8% after halting breast-cancer treatment trial on lowered hopes for success

· *Pfizer stock plummeted as much as 8.2% on Monday after the company halted a phase 3 breast-cancer treatment trial.*
· *The pharmaceutical giant's palbociclib treatment was "unlikely to show a statistically significant improvement" in survival rates, according to a statement made after Friday's market close.*
· *Monday's...