Postmenopausal women with early breast cancer who have undergone successful initial therapy receive five years of treatment with tamoxifen, an antagonist of the estrogen receptor. This placebo-controlled trial investigated whether the administration of letrozole, an aromatase inhibitor, after five years of tamoxifen therapy is beneficial. The trial was stopped because of a statistically significant reduction in the rate of breast-cancer–related events in the letrozole group as compared with the placebo group.

The results of a planned interim analysis were consistent with a stopping rule in the trial's protocol. The median follow-up (2.4 years) is short, but the data persuaded the investigators to reveal the results to the participants.

Many asymptomatic patients with a Wolff–Parkinson–White pattern on the electrocardiogram are at low risk for arrhythmias. However, younger asymptomatic patients with inducible arrhythmias may be at higher risk. This study found that prophylactic catheter ablation of accessory pathways in such patients greatly reduced the risk of arrhythmias.

The findings will affect the treatment of asymptomatic patients with the Wolff–Parkinson–White syndrome; those with inducible arrhythmias should be considered for prophylactic catheter ablation.

Using highly sensitive techniques, researchers identified pathologic prion protein in about one third of muscle and spleen specimens obtained at autopsy from patients with sporadic Creutzfeldt–Jakob disease. Pathologic prion protein has previously been found only in central nervous system and olfactory-nerve tissue from such patients.

The amounts of pathologic prion protein identified in these autopsy studies are very small, but the findings suggest that muscle biopsy, rather than brain biopsy, can be used to diagnose sporadic Creutzfeldt–Jakob disease.

Three closely related infants with a form of severe combined immunodeficiency characterized by the absence of T cells but normal numbers of B cells were found to have an identical germ-line mutation in the CD3 gene. The mutation prevented synthesis of the CD3 protein and was associated with a block early in the development of thymocytes into mature T cells.

The findings in these three patients identify a new form of severe combined immunodeficiency and shed light on the mechanism of T-cell maturation.

A healthy 19-year-old woman comes in for a routine appointment. She is sexually active in a monogamous relationship; her partner uses condoms most of the time. Pregnancy is not currently desired. She has had sexual intercourse several times since her last menses, including an episode of unprotected intercourse four days earlier. A urine pregnancy test is negative. Should emergency contraception be prescribed?

Most people do not survive out-of-hospital cardiac arrest, and those who do may have substantial long-term cognitive and motor impairment. ICDs may avert such events. This review discusses the mechanisms of ICDs, clinical studies of their effectiveness, and management issues.

ICDs have evolved from a therapy of last resort for patients with recurrent cardiac arrest to a management standard for use in the primary and secondary prevention of cardiac arrest.

Eight years ago, Harold E. Varmus, then the director of the National Institutes of Health (NIH), convened a panel to evaluate the status of clinical research in the NIH portfolio and to make recommendations for strengthening this component of the U.S. biomedical research effort. This Sounding Board article examines the outcome of the panel's recommendations.