(NewsNation) — Bonnie and Bob Krall are a married couple who got through the COVID-19 pandemic with relative ease. Bonnie had a couple of mild cases, and Bob had a case that brought no symptoms.

“We were both healthy as can be,” said Bonnie Krall. “We had just finished a giant trip to the Western United States, we came back, and bam, Bob was diagnosed.”

Bob didn’t have COVID but instead two very rare forms of cancer. Then, Bonnie got similar news.

“I had an 8 1/2 pound tumor in my abdomen,” she told NewsNation’s “Elizabeth Vargas Reports.” “I was healthy in December, and by April, they diagnosed the cancer.”

The Kralls are among a growing number of people who had COVID and then developed rare kinds of cancer, often more than one kind.

“We started noticing some very unusual patterns,” said the Kralls’ physician, Dr. Kashyap Patel. He and his colleagues at Carolina Blood and Cancer Care Associates have documented some very concerning links between COVID and cancer:

• A 20-30% rise in new patients
• Multiple patients with multiple cancers
• Couples and siblings developing cancer within months
• Cancer patients relapsing after years of remission

Patel says the inflammation that often accompanies COVID may be key to finding the link to the cancers people are contracting.

“Inflammation triggers many genetic changes in a genome that can create a propensity of developing cancer in certain individuals,” said Patel. “I’m analyzing close to 300 patients’ data on the inflammatory biomarkers in the body with Long COVID antibodies … and if they had an unusual cancer,” he added.

For Bob and Bonnie Krall, at least, the immediate prognosis is good. Bob is in remission, and Bonnie is close to it, she says. But learning exactly why it happened to them may always be a mystery.

“Who knows? How can we ever know that?”