肥満および乳がんに関連した死亡率（Abstract: 503）

肥満は閉経前ER陽性乳がん患者においてのみ実質的に乳がん死亡率を上昇させる
Obesity substantially increases breast cancer mortality only in women with pre-menopausal ER+ disease
70の臨床試験における早期乳がん患者80,000人のスタディにおいて、肥満は閉経前エストロゲン受容体（ER）陽性患者においてのみ乳がん関連死リスクを34%上昇させることが示された。このEarly Breast Cancer Trialists' Collaborative Groupスタディでは、同じ臨床試験で同じ治療を受けた女性の記録を比較した。標準体重、過剰体重、および肥満（20-25、25-30、≧30 kg/m2）は、ボディーマスインデックス（BMI）を用いて定義した。予後に対するBMIの独立した影響を評価するために研究者らは、腫瘍の特徴を腫瘍の大きさやリンパ節への拡がり、および治療に関するあらゆる相違などの結果で補正した。ER陽性閉経前女性患者20,000人において、肥満女性は標準体重の女性よりも乳がん死亡率が3分の1高かった。これは例えるなら、乳がん10年死亡リスクを15%から20%に引き上げることになる。これとは対照的に、ER陽性閉経後女性40,000人またはER陰性女性20,000人いずれにおいても、肥満は乳がんの予後にはほとんど影響しなかった。この研究結果は第50回American Society of Clinical Oncology学会で発表された。
Full Text

A new study of 80,000 women with early breast cancer in 70 clinical trials finds that obesity is associated with a 34 percent higher risk of breast cancer-related death only among the 20,000 pre-menopausal women with estrogen receptor (ER)-positive disease. Obesity had little effect in post-menopausal ER-positive disease or in ER-negative disease.

"Obesity substantially increases blood estrogen levels only in post-menopausal women, so we were surprised to find that obesity adversely impacted outcomes only in pre-menopausal women," said Hongchao Pan, Ph.D., a researcher at the University of Oxford in the United Kingdom. Dr. Pan continued: "This means we don't understand the main biological mechanisms by which obesity affects prognosis."

This Early Breast Cancer Trialists' Collaborative Group (EBCTCG) study compared records from women who received the same treatment in the same clinical trial. Body-mass index (BMI) was used to define normal weight, overweight, and obesity (20-25, 25-30 and ≥30 kg/m2). To assess the independent effects of BMI on prognosis, the researchers adjusted the findings for tumor characteristics such as size and nodal spread, and for any differences in treatment.

Among the 20,000 pre-menopausal patients with ER-positive disease, the breast cancer mortality rate was one-third higher in obese women than in women of normal weight. This would, for example, change a 10-year breast cancer mortality risk of 15 percent into a 10-year risk of 20 percent.

In contrast, obesity had little effect on breast cancer outcome either among the 40,000 post-menopausal women with ER-positive disease or among the 20,000 with ER-negative disease.

"This study is part of the growing body of evidence showing that patients who are obese generally fare worse with cancer— in this case, younger women with breast cancer," explained Clifford A. Hudis, M.D., FACP, ASCO President. "With some two-thirds of our nation's adult population now obese or overweight, there's simply no avoiding obesity as a complicating factor in cancer care. ASCO is working to support physicians and patients in addressing this challenge, and we urge researchers to examine new strategies for reducing obesity's cancer-related toll."

The study was funded by Cancer Research UK, the MRC and the British Heart Foundation.