How best to express oestrogen receptor activity

All these estimates are necessarily unprecise, being based on small numbers. They could be used in connection with speculations regarding the critical age at first use, arguing that a very high ratio between OR* and OR is unlikely, thus making age 18 years an appealing choice. Finally, we do not completely agree with Dr Tomasson when he claims that the two Icelandic studies and the results of the Collaborative Group on Hormonal Factors in Breast Cancer (1996) all show that use ofOC has very little impact on the risk for breast cancer. We feel that there is still a question mark concerning the effects ofOC use at young age. Our study, as well as the one by the Collaborative Group give rise to some concern about this matter. The study of the Collaborative Group also found an increased risk in young users and, to quote the paper, 'The available data for use beginning before age 20 indicate that there is no substantial increase of breast cancer risk in this subgroup more than 5 years after cessation of use, but virtually all the existing information relates to women younger than 45. In the next decade women who began use as teenagers will reach their late 40s and early 50s, when breast cancer is more common. When the new data on the long-term effects of early use become available it will be necessary to re-examine the worldwide evidence'.