Dr. Farid Fata pleaded guilty in the fall to fraud, money laundering and conspiracy charges.
"There is no true justice. You can't undo the past," said Karen Baldwin, whose husband died in 2006 while under the doctor's care. "You can't bring back the dead people we love."
Fata's sentencing hearing began Monday and was expected to last a few days. Many of the victims today wore black. On Tuesday, one member of each family affected was expected to get 10 minutes each to testify about how their lives had been changed by Fata.
"He gave me so much treatment, it stopped my immune system," said Terry Spurlock, 52, of Holly, Michigan, who traveled with other former patients and their relatives on a bus to attend the hearing.
Fata of Michigan's Oakland Township was arrested in 2013 as federal agents raided his offices in the Detroit area and seized his medical records.
A federal criminal complaint said he’d reportedly given "unnecessary chemotherapy to patients in remission" and deliberately misdiagnosed patients in order to defraud the federally-funded health care program of approximately $35 million over a two-year period.
The complaint also alleged that he'd "systematically defrauded Medicare by submitting false claims for services that were medically unnecessary" for patients, which included a variety of cancer and hematology treatments given to people who did not need them.
Prosecutors said that more than 500 patients had received unnecessary treatment.
Steve Skrzypczak said he'd been diagnosed with non-Hodgkin's lymphoma -- and had been ordered to receive treatments including chemotherapy -- even though he didn't have the disease.
During today's hearing, a medical professor who'd examined 25 patient files for the prosecution, called Fata's method of treating cancer patients "over the top," according to The Associated Press.
"The anger, the frustration, that I hope will finally be gone once he [Fata] is sentenced," Baldwin said.
ABC News' affiliate WXYZ-TV in Detroit and The Associated Press contributed to this story.