Issues in the assessment of the pathologic effect of primary systemic therapy for breast cancer

Emerging evidence suggests that induction of pathologic complete response (pCR) after primary systemic therapy (PST) is, at least to some extent, predictive of survival. However, standards for processing surgical specimens and for histopathologic evaluation of the pathologic response to therapy appear to be lacking.

To perform a systematic review of representative articles on this topic, a computerized (MEDLINE) search was undertaken followed by a manual search based on the reference lists of the publications identified.

Several classification systems have been used to assess pathologic response to PST, the term pCR has not been applied in a consistent standardized manner, and only limited information is available about the reliability and validity of these classification systems. However, definitions of pCR can be summarized as follows: near pCR, only focal invasive tumor residues in the removed breast; quasi pCR, total or near total disappearance of invasive tumor in the removed breast; pCRinv, only in situ tumor residual in the removed breast; comprehensive pCR, no evidence of residual invasive tumor in the removed breast; strict pCR, disappearance of all tumor cells in the removed breast; comprehensive pCR (br+n), no evidence of residual invasive tumor in the breast and axillary nodes; strict pCR (br+n), no malignant tumor cells in the removed breast and axillary nodes. Comparison of the use of the term "pCR" in various trials reveals that it is not applied equivalently in these studies.

Assessment of pCR needs to be standardized, with verification for reliability and validity. For now, the non-equivalency in the definition of pCR should be taken into account when comparing the results of PST.