The role of primary systemic therapy (PST) in the treatment of operable breast cancer is currently under intensive investigation in the hope of allowing greater conservation of the breast, and emerging evidence suggests that induction of a pathological complete response (pCR) is at least, to some extent, predictive of long-term clinical response. In this review, we highlight the issues of pathologic evaluation after PST.

We performed a computer-assisted MEDLINE search, and additional references were found in the bibliographies of these articles.

So far, several grading classifications are used to assess pathologic responses after PST, and pCR rates vary from 1% to 54.7% according to the PST regimens employed. However, the term “pCR” has not been applied in a consistent, standardized manner, and the pCR rates appear to depend not only on the differences in the definition of pCR, but also on the extent of tissue sampling and the techniques used for pathologic examination. So far, only limited information is available about the reliability and validity of the definition of pathologic responses.

Assessment of pCR needs to be standardized, and each grading system should be verified for reliability and validity. As a lack of standard for tumor processing and evaluation may result in considerable fluctuation of pCR rates between trials, we should take into account the differences in the definition of pathologic response when comparing the results of PST.