There are approximately 600,000 new cases of breast cancer each year world-wide. Breast cancer is the most common cancer among women in the United States accounting for a quarter of all female cancers and is second only to lung cancer as a cause of cancer-related deaths.Cancer Research UK estimates that alcohol accounts for around 4% of breast cancers in the developed world and that one in eight women will develop breast cancer during her lifetime. Over the past 10 years, the incidence of breast cancer has remained unchanged, although mortality rates have steadily decreased, due to earlier detection and more effective therapy.

Risk factors include age (the risk for developing breast cancer by age 40 is 0.5%, compared with 10% by age 80), as well as lifetime exposure to unopposed oestrogen (early menarche, late menopause, late first pregnancy or prolonged use of oestrogen-based oral contraceptives). Women with certain benign proliferate lesions of the breast, as well as those with a premalignant condition called carcinoma in situ, are also at increased risk for developing invasive breast cancer, and individuals who have already sustained one breast cancer are at increased risk for a second primary tumour.

Germline mutations in the breast cancer genes BRCA1 and BRCA2, present in about 0.1% of the general population, are associated with a high lifetime risk for developing breast cancer at an early age, as is a family history of breast and/or ovarian cancer. Hormonal risk factors are likely to modulate genetic predisposition to breast cancer, although the magnitude of this effect is unknown and inherited mutations are believed to account for approximately 5% of breast cancer cases. Environmental factors, including diet, alcohol intake and obesity, have been suspected but not consistently linked to increased breast cancer risk. However, according to a recent meta-analsis on the effects of alcohol and smoking on breast cancer risk published in the British Journal of Cancer, a woman’s risk of breast cancer increases by 6% for each alcoholic drink.

Researchers combined results from more than 50 studies and included data on around 150,000 women from around the globe. Over 23,000 of these women did not drink and looking at this group separately the researchers could see no significant difference between rates of breast cancer in smokers and non-smokers.

Sir Richard Doll, a co-author of the study, says: "For the first time we have undertaken a study large enough and detailed enough to look at the separate effects of tobacco and alcohol reliably. When we did this we found that drinking, but not smoking, increases the risk of breast cancer." Co-author Professor Valerie Beral, of Cancer Research UK’s Cancer Epidemiology Unit at the Radcliffe Infirmary in Oxford, says: "This research tells us there is a definite link between alcohol and breast cancer and the evidence suggests that the more a woman drinks the greater her risk".

The average alcohol intake for UK women has increased from about 7 grams to 8 grams per day in the last decade, but among women aged between 16 and 24, the proportion drinking more than three drinks per day has doubled from nine per cent to 18 per cent.

Dr Gillian Reeves, a co-author, commented "The balance between the harmful effects of alcohol on breast cancer and its beneficial effects on heart disease depend on a woman’s age. Before about 60, breast cancer is a more important cause of death than heart disease. After the age of 65 or so, when the risk of heart disease becomes much greater than the risk of breast cancer, the benefits of moderate drinking are more apparent." Sir Paul Nurse, Cancer Research UK’s Chief Executive, says: "Large studies of this kind are very important for dissecting the complex causes of cancer. This research doesn’t alter our advice on smoking because we already know that it’s dangerous but it does reinforce our advice that excessive drinking can also be hazardous."

The second study by Dr. Wendy Y. Chen of Brigham and Women’s Hospital and the Dana-Farber Cancer Institute in Boston, Massachusetts was published in the Annals of Internal Medicine.

Based on results from a group of more than 44,000 women, the investigators discovered that women who either drank at least 1-1/2 alcoholic drinks each day or took HRT for at least 5 years appeared to have a 30% increased risk in breast cancer, relative to their teetotaller counterparts who opted out of HRT. The study found that women who drank an average of less than one drink each day showed no increased risk of breast cancer. Chen and her colleagues base their findings on a group of 44,187 postmenopausal women who were followed for 14 years. A total of 1,722 women developed breast cancer. Chen explained that the current study did not investigate how alcohol consumption or HRT could influence the risk of breast cancer, but said that previous research has suggested that both can up the risk by increasing levels of oestrogen in the body.

Chen emphasized that the current findings do not suggest that women need to abandon alcohol all together. "I think it means you should limit it to less than a glass and a half per day," she noted.

The results are put in perspective by the editorial accompanying Sir Richard Doll’s study; I. dos Santos Silva entitled Alcohol, tobacco and breast cancer: should alcohol be condemned and tobacco acquitted? (Br J Cancer 2002;87:) .Dr. Silva concludes: "Alcohol intake . . . is likely to account, at present, for a small proportion of breast cancer cases in developed countires, but for women who drink moderately, its lifetime cardioprotecdtive effects probably outweigh its health hazards." In his editorial, he also points out that moderate drinkers live longer than non-drinkers.