The "Jeopardy!" host said he struggles with feeling like he's a "terrible burden" on his wife of 30 years.
The Supreme Court justice began the treatment in May, in response to a recurrence of cancer.
The longtime "Jeopardy!" host said his treatment was paying off, and he looked forward to returning to the studio.
"I was 36, a nonsmoker, an obnoxious consumer of organic green peppers ... but there it was: a tumor the size of a small city wedged smugly in my left bronchus."
"Tell me how to grieve when we're not permitted to have a funeral... when the precious body of my child disappeared into the back of a funeral home minivan, never to be seen again."
After the too-cute interruption, the four-time Grammy winner shared that his family still has "good days and bad days."
In a rare on-camera interview with "Good Morning America," the "Top Gun: Maverick" star also recalled his on-set reunion with Tom Cruise.
Many cancer patients have had surgeries delayed and treatment procedures changed as the country battles COVID-19.