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The use of the drug tamoxifen in the treatment of early stage breast cancer—as hormone therapy following surgery—is ac- cepted clinical practice. However, the question of how long to continue the drug has been, and still is, a hotly debated topic. The specific concern is, When do the risks outweigh the bene- fits? It is clear that thousands of women who take tamoxifen will live longer and remain disease free longer as a result (7). But tamoxifen has also been associated with an increased risk for second primary cancers (2J). In this issue of the Journal, two large randomized studies, one by the Swedish Breast Can- cer Cooperative Group (4) and the other by the National Surgi- cal Adjuvant Breast and Bowel Project (NSABP) (5), shed light on this very complex question of duration of treatment. The rationale for long-term administration of tamoxifen derives initially from laboratory evidence that mammary tumor development in a mouse model is best inhibited by continuous treatment at an early point after carcinogen exposure (6). Fur- thermore, estradiol can reactivate tumor growth in mice after tamoxifen treatment is discontinued, suggesting that the drug's action is cytostatic (7). However, the development of tamoxifen- dependent tumor growth after several months of treatment has also been demonstrated (8), which indicates that clinical trials are essential to determine the optimal duration of treatment in humans. The hypothesis tested in the two large clinical trials reported here is that increased duration of tamoxifen treatment decreases mortality from breast cancer. Each of these trials asks a different question in regard to treatment duration. The Swedish study looks at 2 versus 5 years of tamoxifen therapy, with the primary end points of event-free survival (which does not include the occurrence of second primary cancers) and over- all survival. The NSABP B-14 study first compares 5 years of tamoxifen with placebo, using the primary end points of dis- ease-free survival (which includes the occurrence of second primary cancers) and overall survival, followed by a second ran- domization to an additional 5 years of tamoxifen or no further treatment. The Swedish study included 3887 patients who were post- menopausal, who had axillary lymph node-negative or -positive disease, and who had estrogen receptor (ER)-negative or -posi- tive tumors. The dose of tamoxifen was either 20 or 40 mg per day. The overall conclusion of the authors is that there is an event-free survival benefit as well as a general survival benefit for women receiving tamoxifen for 5 years versus 2 years. This is apparent for patients with ER-positive tumors (node-negative or -positive disease) and is most pronounced during years 6-8 of follow-up, with a median follow-up of 5Vi years.

betaCarotene and Lung Cancer Promotion in Heavy Smokers--a Plausible Relationship?