STOCK OF his pharmaceutical company, Insys Therapeutics, has quintupled since its May IPO, catapulting him to billionaire-ship at 70. Insys produces drugs to alleviate cancer patients’ symptoms; he’s its founder and executive chairman, and his stake is now worth more than $600 million. He also owns more than $400 million of drugmaker Akorn. The first member of his family to go to college, he arrived in America from India in 1964. His career took off when he joined LyphoMed, a struggling pharma company, in 1978, worked his way up to general manager, turned the business around and sold his share of it in 1990 to net $100 million. He has been a serial entrepreneur ever since. “This is the country you can do it in. Nowhere else,” he tells FORBES.…