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| Study feeds controversy over timing of tumour surgery. 9 September 2003
The phase of a mouse's menstrual cycle can dramatically alter the risk of cancer spreading, say researchers in Canada. The finding fuels the debate over whether women's cancer surgery should be timed to specific menstrual stages. Some studies on breast-cancer patients have found that women whose tumours are removed in a particular phase of their menstrual cycle are more likely to get secondary tumours - called metastases - and die earlier. But other studies have found no such link. Nearly a third of mice injected with skin-cancer cells when their levels of the hormone progesterone was high developed ovarian tumours, reports a team led by Ann Chambers of the London Regional Cancer Centre in London, Canada1. Those injected when oestrogen was high showed no such cancer. "We were so startled," Chambers says. The study implies that other tumours besides breast cancer might be more likely to spread if they are operated on at particular times. This might be particularly crucial for surgery on young tumours which might slough off potentially migrating cancer cells before they would naturally spread, Chambers suggests. The study is important, says Richard Love, who studies breast cancer at the University of Wisconsin in Madison, because it shows that hormones might promote metastasis by working on the tissues in which a drifting cancer cell implants. Until now, most research has focused on how hormones change the tumour itself. But it is too early to consider rescheduling operations, warns breast-cancer researcher Gabriel Hortobagyi of the University of Texas in Houston. The picture may be very different in women from that in mice. "It adds another reason to do a proper clinical trial," he says. Clinical clash The results of clinical studies about menstrual phase and metastasis are conflicting, mainly because data are often gathered retrospectively, and menstrual phase was not precisely recorded. What's more, the rolling menstrual cycle, with its subtly shifting hormone patterns, is difficult to divide into neat stages. Large-scale prospective studies are now under way in the United States in which women's blood hormone levels are measured accurately before breast-cancer surgery. "Everything else is just background noise," says Hortobagyi.
Researchers are not sure how shifting levels of oestrogen and progesterone might trigger metastasis. Chambers speculates that the hormones alter the structure of the ovary or stimulate the growth of blood vessels, making them more receptive to implantation or development of cancer cells. If the protective hormones - or other molecules - can be identified, they might even be administered before surgery, Chambers suggests, an idea that might be tested using her mouse model. | |||||||||
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