[Complete response after neoadjuvant therapy : How certain is the pathology?]

Histopathologic evaluation of tumors after neoadjuvant therapy is performed by tumor regression grading (TRG) systems, which reflect the proportion of vital residual primary tumor in relation to the previous total tumor. The World Health Organization (WHO) tumor grading is replaced by TRG in tumor classification. The histopathological work-up of a tumor is based on the criteria of the TNM classification even after neoadjuvant therapy. A uniform TRG does not exist. For various tumors TRGs based on the tumor entity have been established, consisting of a 3-stage or 5‑stage grading system. Complete histopathological tumor regression is only present if no vital tumor cells are detectable in the histopathological examination of the primary surgical specimens (primary tumor and accompanying locoregional lymph nodes) and there are no distant metastases.