Obesity and cancer outcome : The Lancet
Obesity and cancer outcome
12
million Americans are cancer survivors and a staggering two-thirds of
Americans are currently considered overweight or obese. On April 3, the
National Cancer Policy Forum of the US Institute of Medicine released a
welcome report entitled The Role of Obesity in Cancer Survival and Recurrence.
Many epidemiological studies have identified obesity as a factor in
cancer risk and prognosis. Obesity is associated with higher cancer
incidence, recurrence, progression, and death. The report emphasises how
little is still known about the precise cellular mechanisms that link
obesity with cancer.
Adipose tissue can
behave as an endocrine organ by generating hormones, growth factors, and
cytokines that can disrupt regulation of cell growth and survival—the
hallmark of malignancy. Knowing the precise cellular targets involved in
this interplay could lead to targeted therapeutic approaches for
controlling both cancer and obesity. For example, appropriate animal
models could allow investigation of mechanisms of obesity and diabetes
in precise genetic models of human cancers.
What
is not yet known is whether weight management changes the prognosis and
outcome in different cancers. The simple solution of tracking
individuals' BMI and bodyweight during clinical trials to analyse effect
on cancer outcomes needs to become standard practice. Another area of
clinical controversy is related to proper chemotherapy dosing in obese
cancer patients. Total body-surface area is used to calculate the
chemotherapy dose, which does not take into account the body's
composition (such as an individual's fat percentage). This approach
often leads to suboptimum doses of chemotherapy.
But
the most important lesson of this report comes from the basic science
of obesity-associated cancer risk. Our population-level responses—which
have largely failed—are based on a far too simplistic understanding of
how obesity contributes to cancer. To address this challenge demands not
more poorly thought out intervention trials.
Instead, we need greater
understanding of the biological mechanisms underpinning cancer and
obesity.
