LONDON, Apr 28, 2005 (United Press International via COMTEX) -- A British study of over 700,000 women shows certain types of hormone-replacement therapy or HRT increases the risk of cancer womb cancer report researchers.

The study looked at estrogen-only HRT, combined HRT (containing progestagen and estrogen) or tibolone, a synthetic HRT. Participants in the study were 50 to 64 years of age and without a history of cancer. None of the participants had had a hysterectomy and over half of the women had used some form of HRT. By the end of the study 1,320 womb cancers were diagnosed in the participants.

The researchers found that estrogen-only HRT and tibolone increased the risk of cancer of the womb as compared to those who never used HRT. The longer one used tibolone the higher the risk.

Obesity elevates the risk of womb cancer in women and, for these women combined HRT actually reduced the cancer risk. In normal weight women, a technique called cyclic-combined HRT increased the cancer risk.

Prior studies have shown, however, that combined HRT increases the risk of breast cancer.

The study, done by Cancer Research UK and University of Oxford, appears in the current issue of The Lancet.