The 50-gene PAM50 panel known as Prosigna can classify breast cancer into luminal A, luminal B, basal, or HER2 molecular subtypes using mRNA expression, explains Francisco J. Esteva, MD, PhD. The test precisely measures RNA in tumors to identify not only intrinsic subtype but also a score to risk-stratify patients into low-, intermediate-, or high-risk groups.

This classification is similar to that of the other available tests, such as Oncotype DX, Esteva notes. A randomized trial using both Oncotype DX and Prosigna found a good correlation between low- and high-risk classifications between the 2 tests. However, Prosigna had fewer patients classified into the intermediate-risk category, which has historically been a difficult group to treat, Esteva notes.

In the study, 1017 samples from postmenopausal women with HR-positive early stage breast cancer treated with 5 years of endocrine therapy were examined using Oncotype DX or Prosigna. When considering tumor size and clinical treatment scores, Prosigna placed 61% of patients in the low-risk group, 22.3% in the intermediate group, and 16.6% in the high-risk group compared with 59.5%, 27.2%, and 13.3% with Oncotype DX, respectively.