By Nicole Weisensee Egan
April 22, 2013 12:00 PM

For the past 4½ years, Andrew Madoff has tried his best to forget he is the son of one of the most hated men in America. He cut off all contact with his father, started up a business in a completely different field with his fiancé e and cooperated in a tell-all memoir he hoped would clear his name once and for all. “I feel horrible for the people whose lives have been destroyed by my father’s crimes,” says Andrew, 47. Not even finding out he once again has mantle-cell lymphoma, the rare and deadly cancer he successfully fought off 10 years ago, was enough to change his mind about reconciling with his father, Bernie. “I will never forgive him for what he did,” says Andrew in an exclusive interview with PEOPLE. “He’s already dead to me.”

Andrew’s health crisis is the latest tragedy in a family that once seemed to have it all. In March 2009 Bernie, 74, pled guilty to running a $65 billion Ponzi scheme and defrauding tens of thousands of people out of $20 billion. He is currently serving a 150-year sentence at a federal prison in Butner, N.C. Andrew and his older brother Mark, both of whom were traders in Bernie’s market-making operation, which was separate from his investment-advisory business, turned their father in to authorities in December 2008, after he confessed to them. “We never hesitated,” says Andrew. “The decision was at the same time the easiest decision I ever had to make and the hardest.”

The aftermath tore the remaining Madoffs apart. The brothers stopped speaking to their mother, Ruth, angry that she stood by Bernie’s side. And each son dealt with the scandal differently. Andrew refused to read news stories or watch TV, instead choosing to “embrace” his friends and other family, he says. “Having somebody to talk to, a shoulder to cry on,” he says, “is the difference between life and death.” Mark turned inward, obsessively reading everything he could get his hands on about his father’s crimes. Two years later he committed suicide. “My brother did not like to lean on his friends for support,” says Andrew, “and he suffered alone because of it.”

After Mark’s death, however, Ruth and Andrew slowly began reconciling. “We did it gradually,” says Andrew, “with a lot of talking and working through the challenges” (see box). Their relationship was fully back on track by the time he found out his cancer had returned—this time stage four—during his yearly checkup last October. “I was blindsided,” he says quietly. “I had no symptoms. I felt fine.” Andrew believes the stress of the last few years at least partially opened the door for his cancer. “One way to think of this is the scandal and everything that happened killed my brother very quickly,” he says. “And it’s killing me slowly.”

And yet, he vows not only to fight cancer but to beat it: For starters, he’s undergoing several brutal rounds of chemotherapy, followed by a stem-cell transplant in late April. “The transplant is a scary thing,” he says. “My cousin died from the side effects of his stem-cell transplant, so that’s on my mind.” In January he cut back his hours at Black Umbrella, the disaster-preparedness company he started with his fiancée, Catherine Hooper, 40. He limits his outings to one a day and takes whatever precautions necessary to protect his weakened immune system, whether it’s keeping a bottle of Purell handy or forgoing kisses. A positive attitude, he says, is also key. “I’m always very focused on the things that are good in my life—of which there are many,” he says. “I have no choice but to fight my way through and live.”