It's a particularly important link in post-menopausal women.
When 60-year old Susan Aichele of South Philadelphia was diagnosed with Stage 1 breast cancer, this spring, her doctors at Jefferson Hospital asked her to enroll in an obesity trial.
Susan says, "They said it was to reduce calories and you would have less complications."
With the trial, doctors are also testing a theory that cutting calories by 25-percent greatly reduces the risk of recurrence.
Dr. Richard Wender of Thomas Jefferson University Hospital says, "The research that we have so far, it most strongly tells us that it's your weight that matters."
Later this month, Dr. Wender will become the American Cancer Society's chief cancer control officer.
He says when the A-C-S was founded in 1913, doctors knew virtually nothing about cancer.
"We didn't understand the very nature of the disease, that it was caused by mutations in cells," says Dr. Wender.
But so many milestones have been set since then:
Researchers created the first chemotherapy in 1947, in 1971, they started using mammograms, and since they've continued to identify risk factors.
For Jefferson's obesity trial, Susan Aichele keeps an online food and exercise diary. She walks and takes yoga and she's lost 30 pounds.
"So will you continue the lifestyle changes?" we asked. Susan quickly replied, "Oh yeah, oh yeah."
Her goal is to reach a healthy weight, but already she's seeing benefits.
"My estrogen level because my tumor was estrogen-based, that reduced a lot so everybody actually was really happy. My other numbers came down, my cholesterol, my sugar levels," she told us.
Dr. Nicole Simone, the lead researcher on the study, says, " It's something that they can do for themselves to help, which is empowering."
For all of the advancements in breast cancer research, it remains the leading cause of cancer in women.
If you'd like to join the fight against the disease, you can join Ali at the annual Making Strides Walk. We step off this Saturday, October 19th at 8am at Memorial Hall in Fairmount Park.