US Food and Drug Administration (FDA) announced last June 9, 2011, that it has revised the Warnings and Precautions section of the labels for the 5-alpha reductase inhibitor (5-ARI) class of drugs to reflect new safety information about the increased risk of being diagnosed with a more serious form of prostate cancer (high grade prostate cancer). Drugs belonging to this class include finasteride 5mg (Proscar) and dudasteride (Avodart). Both drugs are currently approved for the management of benign prostatic hyperplasia (BPH).

The agency in its safety announcement mentioned, "This risk appears to be low, but healthcare professionals should be aware of this safety information, and weigh the known benefits against the potential risks when deciding to start or continue treatment with 5-ARIs in men."

A cancer cell is often described by both stage and grade. Staging refers to how far the cancer or neoplastic cells has spread and grading is a system of classification relying on the microscopic appearance of cancer cells and how quickly said tumor is likely to grow and spread. It describes how abnormal the tumor cells appear or how different it appears from normal cells, a measure of differentiation.

Tumor grades are described by pathologists based on the microscopic appearance using four (4) degrees of severity. As for prostate cancer, the Gleason system, score ranging from 2 to 10, is also being utilized. Both system states that well-differentiated cells or low-grade tumors are generally considered the least aggressive in behaviour while tumors described as poorly differentiated are high-grade tumors and are deemed to be most aggressive in behaviour.

Two large and randomized controlled trials, the Prostate Cancer Prevention Trial (PCPT) and the Reduction by Dutasteride of Prostate Cancer Events (REDUCE) trial, were the basis of the new safety information of FDA. Both trials showed an overall reduction in prostate cancer diagnoses with finasteride 5 mg and dutasteride treatment. However, both trials also manifested an increased incidence of high-grade prostate cancer with the said treatment.

FDA report also mentioned that drugs in this class (5-ARIs) include finasteride (marketed as Proscar [finasteride 5 mg] and Propecia [finasteride 1 mg]) and dutasteride (marketed as Avodart). Dutasteride is also available in combination with tamsulosin, under the brand-name Jalyn. Proscar, Avodart, and Jalyn are all approved to improve symptoms of an enlarged prostate gland (benign prostatic hyperplasia or BPH). Propecia, on the other hand, is approved to treat hair loss in men.