Within hours of being placed on leave, Ms. Bisconti accessed more than 200 confidential documents and materials, the lawsuit alleges. She was fired on Dec. 31, the lawsuit says.
Ms. Bisconti did not return messages seeking comment.
The lawsuit is a bizarre chapter in the career of Mr. Stephenson, who in 1988 founded Cancer Treatment Centers, which has about $4 billion in annual revenue, according to a person familiar with the company's finances. Midwestern Regional Medical Center in the northern suburbs is one of the company's five specialty hospitals nationwide.
Despite the company's growth, Mr. Stephenson, a Barrington resident, kept a low profile until December, when the Washington Post reported that he played a key role in the ouster in September of Richard Armey as chairman of FreedomWorks and funneled $12 million to the tea party's PAC before the November election.
The dispute with Ms. Bisconti began in June, when she allegedly asked Mr. Stephenson for $250,000 due to financial difficulties that are not specified in the complaint.
The company didn't regularly loan money to employees, but Mr. Stephenson agreed to loan her $50,000 because of her longtime ties to the company, sympathy for her medical history and a recent divorce, the complaint says.
Three months later, Ms. Bisconti again asked Mr. Stephenson for money. When he refused, she threatened to talk to the press if he didn't pay her $10 million, the lawsuit said.
On Jan. 15, through her attorney, she upped her demand to $49.5 million, the complaint says.
The company says it wasn't clear what Ms. Bisconti would tell the media but alleges she “had every intention” of disclosing trade secrets, including strategic plans and financial information, none of which was publicly available.
Ms. Bisconti's lawyer, Maureen Maffei, told the company her demand was based on her belief that the company had made a large payment to a former employee, the complaint says.
Ms. Bisconti contended she should be paid 150 percent of what the former employee was allegedly paid, according to Ms. Maffei, of Lisle-based law firm Coman & Anderson PC.
The company denies those allegations, saying Ms. Bisconti falsely accused the employee of embezzlement. Ms. Maffei did not return messages to comment.
Ms. Bisconti is accused of violating her confidentiality agreement, common contracts that are intended to protect company secrets, but can also tighten the hold on what employees can say and do with their work.
Employers “don't want whatever their business strategies are or whatever their trade secrets might be . . . disclosed,” said Arthur Ehrlich, a partner at Chicago-based Goldman & Ehrlich, which specializes in employment law.
Ms. Bisconti joined Cancer Treatment Centers in 2008 as head of Gateway for Cancer Research, which funds phase 1 and phase 2 human clinical cancer trials. The company called Ms. Bisconti the “ambassador” of the charity, overseeing the organization's strategy and direction, raising funds and forging partnerships to advance its mission, the lawsuit says.
Before she was fired, the company offered her a severance package, which she never accepted or rejected, the company alleges.
A spokeswoman for Cancer Treatment Centers declined to answer questions about the lawsuit but in a statement said Ms. Bisconti was a “valued member” of the company's leadership team.
“We are at a loss for understanding why she has taken these actions,” the statement said. “The statements made in our filing are accurate, and we therefore have no further comment on this matter pending the outcome of the court's review.”
Mr. Stephenson started the company after the death of his mother, aiming to provide traditional surgery and chemotherapy alongside alternative methods, such as acupuncture and laughter therapy, an approach his mother didn't receive, the complaint says.
The privately held company, which does not publicly disclose revenue, treats more than 6,000 patients a year.
The 73-bed Midwestern Regional Medical Center in Zion had $504.1 million in net patient revenue in 2011.