Viruses don't often come with silver linings, and infections don't generally lead to positive health effects. But during the pandemic, some doctors anecdotally began noticing that some people with cancer who got very sick with COVID-19 saw their tumors shrink or grow more slowly.

"We didn't know if it was real, because these patients were so sick," says Dr. Ankit Bharat, chief of thoracic surgery at Northwestern University. "Was it because the immune system was so triggered by COVID-19 that it also started to kill cancer cells? What was it?"

Bharat and his team decided [to] conduct a study to find out if the seeming "benefit" of COVID-19 for these cancer patients could teach them anything about a potential new way to fight cancer -- or if it was simply a red herring.