The CancerWeb Report, What's New In Cancer: July, 1996
Colorectal Cancer

• Is there an increased risk from using oral contraceptives or hormone replacement therapy? - Use of oral contraceptives and replacement estrogens is widespread, and with this has come concern over potential cancer-inducing side-effects. The evidence has been conflicting, but the more recent studies are tending to discount the risk, at least for some cancers. For example, a group of researchers Barcelona, Spain, and Milan and Aviano in Italy, reported in the June, 1996 issue of the British Journal of Cancer that there was no evidence of increased risk of colorectal cancer, indeed the results suggested a lowered risk, in those (709 subjects in all) taking these estrogen-containing medications. For women who had used oral contraceptives at any time, the odds ratio (risk) of colorectal cancer was reduced to 0.58 compared with matched controls; in those with over 2 years of use the ratio was 0.52. In those who had ever used hormone replacement therapy, the odds ratio was 0.40, breaking down to 0.46 for less than, and 0,25 for more than 2 years' use. (Fernandez, Br J Cancer 73:1431, 1996)

  Editor's Comment: - The authors discuss the results in relation to the lower incidence and mortality from this cancer among women than among men. While the results they obtained are reassuring, and confirm some earlier studies with respect to colorectal cancer, they do not address the more frequently-raised concern about hormone-dependent cancers of the breast or uterus. With these tumors there is certainly no question of reduced risk, although any increase in risk may be less than once feared.

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• Fat levels in the diet do not affect late stages of colon carcinogenesis - While there is a body of experimental evidence to back up the indication from human epidemiology studies that high-fat diets promote colon cancer development, there is no evidence regarding whether this fat effect comes early or late in the overall process. A study carried out in rats by researchers at the University of Manitoba in Canada, examined the effect of feeding high- and low-fat diets at different time periods to rats given the carcinogen, azoxymethane. They found that feeding a high-fat diet early in the process gave an increased incidence of tumors and that they grew to a larger size. On the other hand, there was no effect of dietary fat given at later stages. Early preneoplastic changes also showed the same relationship to timing of the diet as did the tumors. (Bird, Cancer Res 56:2896, 1996)

  Editor's Comment: - There has been an assumption that dietary effects on cancer development are late or end-stage effects. This is probably because they appear to be related to the second, so-called promotion phase of carcinogenesis, rather than the initial event. However, it should not be forgotten that actual appearance of abnormal tissue and subsequently of overt tumors only occurs after many hidden processes have been completed, and these represent not just initiation but many or even most of the steps in promotion.

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• Surgery for lung metastases from colorectal cancer - Individual cancers show a predilection for metastasizing to particular organs. Lung and liver are "favored" sites for colorectal cancer. Provided there are only a few metastases, surgical removal may be a feasible option for eliminating the tumor. Researchers at the Institut Mutualiste Montsouris Choisy, Paris, and the Institut Gustave Roussy in Villejuif, France, described their results for surgical removal of isolated pulmonary metastases in an article in the July, 1996 issue of the Journal of Clinical Oncology. Among 86 patients with colon or rectal cancers who underwent thoracic surgery, the 5- and 10-year survival rates were 24% and 20%. Complete resection, less than two metastases, and a normal preoperative value for preoperative serum carcinoembryonic antigen (CEA), a cancer marker, were predictive of longer survival; 5-year survival was estimated as 60% for those with normal CEA. (Girard, J Clin Oncol 14:2047, 1996)