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A central tenet of neoadjuvant clinical trials is that tumor response, as a surrogate end point, should be strongly correlated with long-term patient survival.1,2 Otherwise, the value of neoadjuvant treatment would be to convert a tumor to operability or to increase the probability of conservative surgery. However, a close association between pathologic response to treatment and subsequent survival establishes neoadjuvant treatment as a method for clinical trials including operable disease to evaluate promising treatments more purely in terms of direct tumoricidal activity and without confounding variables of natural history and subsequent treatments. Indeed, pathologic complete response (pCR) has been adopted as the primary end point for neoadjuvant trials because it has consistently been associated with long-term survival in neoadjuvant trials using different chemotherapy regimens of variable treatment duration.3-12 If pCR is achieved using current therapies, one can anticipate more than 90% probability of disease-free survival within the first decade of follow-up.

Communication between surgeon, radiologist, and pathologist is very important for accurate definition of pathologic response of a patient's breast cancer. The macroscopic appearance of residual tumor can be deceptive in a resected breast specimen, so pCR could be falsely ascribed if the residual tumor bed was not correctly identified and sampled, such that a different area of breast tissue was submitted for histopathologic study. Effective use of the pathology requisition form (clinical history section), electronic medical record, placement of metallic indicators in the tumor bed at the beginning of treatment, and conservative surgical resection (lumpectomy) contribute to more accurate gross and microscopic pathologic assessment of response in the primary tumor bed. We find that specimen radiography with radiologic-pathologic correlation is particularly helpful to identify the tumor bed and to map its extent and margin status, particularly if metallic indicators have been placed in the tumor bed.

Although it is generally held that a definition of pCR should include patients without residual invasive carcinoma in the breast (pT0), the presence of nodal metastasis, minimal residual cellularity, and residual in situ carcinoma are not consistently defined as pCR or residual disease (RD).12-15 When there is no residual invasive cancer in the breast, the number of involved axillary lymph nodes is inversely related to survival.11 Conversely, patients who convert to node-negative status after treatment have improved survival, even if there is RD in the breast.16 This supports the concept that pathologic response in the regional lymph nodes is as important as response in the primary tumor bed. Consequently, the combination of tumor size and nodal status after neoadjuvant treatment is prognostic.17 No evidence indicates that residual in situ carcinoma alone increases risk of future distant relapse.12,18,19 However, residual ductal carcinoma in situ (DCIS) is relevant for local control, and so resection specimens are carefully evaluated for residual DCIS and margin status just like any breast cancer specimen. Therefore, the most appropriate definition of pCR with respect to prognosis is lack ...

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