Robert W. Duggan, the Church of Scientology’s biggest donor and the chief executive officer of Pharmacyclics Inc., which makes an experimental treatment for chronic lymphocytic leukemia, has become a billionaire after the company’s shares tripled in a year.

Pharmacyclics’ medicine, called ibrutinib, inhibits an enzyme that promotes cancer growth. It helped control the malignancy in 68 percent of 116 patients who hadn’t been previously treated for the blood cancer, the Sunnyvale, California-based company said in a December statement.

“It’s not just promising, it has those unique profiles of looking very efficacious but also really safe,” said John McCamant, editor of Medical Technology Stock Letter, in a phone interview. “That is very rare in cancer drugs.”

Duggan, 68, has made hundreds of millions of dollars investing in and selling companies such as a bakery chain, a European billboard operation and a robotic surgery innovator. He has a net worth of at least $1.2 billion, according to the Bloomberg Billionaires Index, and has never appeared on an international wealth ranking.

“It is our collective desire to usher in a new era of patient friendly, body harmonious, medicinal therapy to cancer patients in need. While much work remains, we are off to a very good start,” Duggan said in an e-mail on Tuesday.

Johnson & Johnson

Ibrutinib, which is delivered by pill and is in Phase III drug trials -- the last hurdle before market introduction -- is part of a new class of medicines for chronic lymphocytic leukemia, or CLL, a cancer that strikes about 16,000 Americans a year at a median age of about 72.

The goal is to use the drug without chemotherapy, a standard treatment that can be too toxic for some elderly patients. Ibrutinib may generate as much as $5 billion a year if approved for CLL and other blood cancers, said Michael Yee, an RBC Capital Markets analyst, in December.

In December 2011, New Brunswick, New Jersey-based Johnson & Johnson said it would pay Pharmacyclics, which Duggan took control of in a 2008 boardroom coup, as much as $975 million to fund getting the drug to market in exchange for half the profits generated globally.