Surrogate end-points or primary outcomes in clinical trials in women with polycystic ovary syndrome?

There are multiple surrogate variables in polycystic ovary syndrome (PCOS), including biometric and biochemical parameters. The number of surrogate variables and their poor validity in relationship to primary clinical end-points pose major problems to conducting a trial in women with PCOS. The aim of this review is to discuss the use of surrogate variables compared with primary clinical end-points in women with PCOS. Arguably the best documented correlation between a surrogate variable and a primary clinical end-point is that between ovulation and pregnancy in women with PCOS. Good correlation has been noted between the increase in ovulation frequency with clomiphene citrate and the chance of pregnancy in women with PCOS. However, ovulation cannot be equated with pregnancy, as a host of other factors may affect the true outcome of interest: a healthy liveborn child. Pregnancy and an improvement in hirsutism are clinical end-points that have been successfully studied in past and ongoing clinical trials in women with PCOS. Many other clinical end-points, such as endometrial cancer and cardiovascular disease, are rare in premenopausal women with PCOS, and may not be suitable as the primary outcome of clinical studies. Future multicentre trials in women with PCOS should focus on primary clinical end-points.