Doherty said she knew her most recent diagnosis would be made public soon because her health struggle is mentioned in a lawsuit she has filed against the insurance company State Farm.
"I'd rather people hear it from me," Doherty said. "I don't want it to be twisted. I don't want it to be a court document."
Doherty says in her lawsuit that the insurer denied claims she made after her house was damaged in the Woolsey Fire, which devastated parts of Southern California in 2018.
"I communicated with my insurance company. I called. I got passed around from claims adjuster to claims adjuster, so I ended up suing State Farm," Doherty said. "And the result has been one of the most horrific processes I have ever been through."
State Farm said in a statement to NBC News that the company empathizes with Doherty's "health issues, and wish her a full recovery," but "we strongly believe we have upheld our commitment to our customer and have paid what we owe on this claim. We are prepared to defend our position in court."
Doherty said she is taking on State Farm because "I want to be remembered for something bigger than just me."
"I'm taking a stand for all of us," she said, "through this lawsuit and by saying enough is enough, with big business and corporations running the little person over."
Attorneys for Doherty said they don't believe the "pertinent information" of the actress' complaint ever went beyond "a low-to-mid-level corporate attorney" before she spoke to ABC.
"We have to believe higher level executives would not have rushed to the same unreasonable, unreasoned and callous positions that have cost Shannen dearly in time, energy and emotional well-being all while suffering a terminal illness," the attorneys said in a statement Wednesday.
Elisha Fieldstadt is a breaking news reporter for NBC News.