Breast cancer trials face costly long-term follow-up needed to detect overall survival differences among patients with relatively indolent malignancies. So you may have noticed that complete pathologic response rates (pCR) are becoming the new PSA of breast cancer trials. In the face of the negative ETNA trial reported last week, this companion editorial highlights some of the pitfalls of using pCR as a surrogate endpoint. Especially among hormone-receptor(+) breast cancers that are often better characterized with alternative strategies such as the PEPI. So while sometimes surrogates are simply the most feasible option, make sure to avoid a surrogacy faux pas.