Gillian Reeves and her colleagues have studied whether there is a relationship between body mass index (kg/m1) and cancer incidence and mortality. They studied a large group of 1.2 million UK women recruited into the Million Women Study, aged 50-64 during 1996-2001, and followed up, on average, for 5.4 years for cancer incidence and 7.0 years for cancer mortality. They looked at the Relative risks of incidence and mortality for all cancers, and for 17 specific types of cancer, according to body mass index, adjusted forage, geographical region, socioeconomic status, age at first birth, parity, smoking status, alcohol intake, physical activity, years since menopause, and use of hormone replacement therapy.
45 037 incident cancers and 17 203 deaths from cancer occurred over the follow-up period. Increasing body mass index was associated with an increased incidence of endometrial cancer (trend in relative risk per 10 units=2.89, 95% confidence interval 2.62 to 3.18), adenocarcinoma of the oesophagus (2.38,1.59 to 3.56), kidney cancer (1.53, 1.27 to 1.84), leukaemia (1.50,1.23 to 1.83), multiple myeloma (1.31,1.04 to 1.65), pancreatic cancer (1.24, 1,03 to 1.48), non-Hodgkin’s lymphoma (1.17,1.03 to 1,34), ovarian cancer (1.14,1.03 to 1.27), all cancers combined (1,12,1.09 to 1.14), breast cancer in postmenopausal women (1.40, 1.31 to 1.49) and colorectal cancer in prernenopausal women (1.61,1.05 to 2.48). In general, the relation between body mass index and mortality was similar to that for incidence. For colorectal cancer, malignant melanoma, breast cancer, and endometrial cancer, the effect of body mass index on risk differed significantly according to menopausal status.
They concluded that increasing body mass index is associated with a significant increase in the risk of cancer for 10 out of 17 specific types examined. Among postmenopausal women in the UK, 5% of all cancers (about 6000 annually) are attributable to being overweight or obese.
They suggest that for endometrial cancer and adenocarcinoma of the oesophagus, body mass index represents a major modifiable risk factor; about half of all cases in postmenopausal women are attributable to overweight or obesity
Association with adenocarcinoma of the oesophagus makes sense as acid reflux will be a potent irritant and hence a stimulus for malignant change. The endometrial cancer
Reeves et al 2007 Cancer incidence and mortality in relation to body mass index in the million women study: cohort study. BMJ vol 335 pp 1134-9
Calle 2007 Editorial Obesity and cancer BMJ vol 335, pp 1107-8
Maybe the other side of this story is important. Malignant change is reduced by decreased energy intake. That it is not so much the obesity but the nutritional load and the metabolic stress incurred.

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Martin Eastwood

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