One reason this tumor grew so big over approximately two decades is that Linda never sought a second opinion about her unexplained weight gain. "Just because you have a doctor for 20 years like I did and trusted him, make sure you have it checked out [again]," she says. "Second, third, fourth."

Dr. Oz says while getting a second opinion can feel like you're breaking a "precious covenant" with your doctor, it really can be critical to your health. "I tell you right now, when you go to get a second opinion, you're teaching me," Dr. Oz says. "[It] doesn't just change your care, it changes the care of everybody else I take care of in so many ways."

Those patients who do get second opinions, Dr. Oz says, tend to see dramatic differences. "It turns out that only 10 percent of us get second opinions," he says. "But when you get them, one-third of the time they will change your diagnosis or your therapy. I don't care how good the doctor is. One-third of the time, a different doctor is going to have a different take on what's going on—and that's an insight that we can never forget."