Grand Rounds: Where do we stand in the battle against breast cancer?

In the first installment of our new medical series, Grand Rounds, we take a look at breast cancer -- a disease that will affect one in eight women in their lifetime. Grand rounds is the practice of senior medical professionals who teach other doctors about advances in health care and treatment.

Dr. David Agus is a leading cancer expert and head of University of Southern California's Westside Cancer Center. He has presented grand rounds for more than two decades around the world. Agus joined "CBS This Morning" to discuss the latest technology, treatments and research on the disease.

The rate of deaths from breast cancer has plunged nearly 40 percent in the U.S. from 1989 to 2015.

"We're screening, people are getting mammograms like they should and we're also getting better at treating it. Early breast cancer, when you take it out and then give certain treatments, you can dramatically reduce the rates of recurrence and that's equaling more people surviving this horrible disease," Agus said.

Agus said it's a "wild time" to be doing what he does with the rapid advances of technology that enables doctors to analyze and target genes.

"We call that molecularly targeted therapy and it's out there and it's working and saving lives. And the newest form is called immunotherapy, which is blocking the 'don't eat me' signal that's on the cancer and allowing the patient's own immune cells to attack the cancer," he said.

According to Agus, about 5 to 10 percent of women have a genetic mutation that puts them at a significantly higher risk for developing breast cancer. Now, there are genetic tests you can buy for $99 that screen for the gene.

"To me it's a no-brainer. I mean you don't get false positives with this test and knowledge is power," he said. "When Angelina Jolie very heroically said 'I have the faulty gene,' it opened the doors to say it's OK to actually look and to talk about it."

One of the biggest mysteries about breast cancer is what causes it in the first place.

"We don't know is the true answer, but the lobules that make milk -- they can get cancer and we start to see it increase by decade. In the 20s it's rare, going up to the 70s and 80s it's much more common," he said. "I think the biggest unanswered question is why does it happen."