George Karadsheh, who worked for Dr. Farid Fata’s Crittenton Cancer Center in Rochester Hills, Michigan, said he started asking questions after staffers kept leaving the practice. When Karadsheh learned that a different oncologist in the practice was quitting, he said the doctor told him it was because Fata was administering chemotherapy to patients who didn’t need it.
“[This doctor] explained that Dr. Fata was actually administering chemotherapy to patients without need,” Karadsheh told ABC News "Nightline." “He was also explaining that patients who were on hospice were taken off hospice and put on chemotherapy, put back on chemotherapy. He also pointed out that patients who were receiving chemotherapy without disease were receiving it to the very last day of life. So at that point I discovered that there may be some issues there.”
"It was so difficult to believe," Karadsheh said. "Here is a physician whose background is second to none in Michigan... I had never had a patient complain that there was a problem with a reaction to a drug or whether it was necessary."
Fata, 50, was sentenced to 45 years in federal prison today after pleading guilty last year to fraud, money laundering and conspiracy charges.
“I’m relieved that Dr. Fata has been held accountable,” Karadsheh said. “But I’m also very sad because I feel the patients endured pain and suffering that’s going to last far longer than the sentence that was imposed upon Dr. Fada.”
At least 553 victims had been identified, with Fata often prescribing treatments for cancer they didn’t have.
In the Detroit federal courthouse Fata sobbed as he spoke prior to sentencing. Speaking to victims of his treatment and their families in attendance, Fata said he had violated the Hippocratic oath and caused "anguish, hardship and pain."
"I misused my talents, yes, and permitted this sin to enter me because of power and greed," Fata told the court.
Earlier this week numerous former patients spoke against the doctor. Some of the victims who spoke never had cancer, others were over-treated and some had treatment for different cancers than the ones for which they were diagnosed because it brought in more money.
One of those victims was 53-year-old Monica Flagg.
“I was feeling fine,” Flagg told "Nightline." “I continued to feel fine until I started some of my treatments with him.”
Flagg said Fata diagnosed her with myeloma, a cancer of the plasma cells in bone marrow, in July 2012. She said she endured multiple rounds of unnecessary testing, bone marrow biopsies, medication and one chemo treatment under his care.
“Other than the physical, or the emotional stress, I don’t know what side effects are anymore,” she said. “It’s very disturbing.”
When Fata gave her the diagnosis, Flagg said he reassured her that they had caught the cancer early but that she would need “a lifetime maintenance dose of chemotherapy.”
“Everybody we knew loved him and I just, from the day I met him, did not like him,” she said.
“He read my chart, looked at me very strangely, I’ll never forget the look that he had when he looked at me,” Flagg said. “He came back the following day and said to me, ‘I want you to know, I work for Dr. Fata. You’re 51, you’re extremely active, you’re a professional, you don’t have cancer and you need to not ever go back to Dr. Fata.”
After months of feeling like something was wrong, Flagg said she was “ecstatic” to hear that she was cancer-free, and then angry to learn that she had been healthy all along. There are many nights, she said, that she still gets upset thinking about her ordeal.
“It’s just heartbreaking,” she said. “I did one chemo treatment. The others did so many that they’re practically dead anyway.”
When asked if he feels like a hero, Karadsheh said the patients are the real heroes.
“They had to endure incredible, horrific treatments that left them incapable of having normal lives and some actually did not recover,” he said.
ABC News' Ron Claiborne, Brandon Baur, Catherine Cole and Gillian Mohney contributed to this report