E. Strong (ed.). Gastric cancer. Principles and practice. Springer (2015)
Although grading systems for tumor response have not been established, response of tumor to previous chemotherapy or radiation therapy should be reported. The assessment of pathological response to neoadjuvant therapy involves both the gross and the microscopic examination of the resected surgical specimen. At the microscopic level, a positive treatment-related effect is observed as abolition of the malignant epithelium and replacement by dense fibrosis or fibroinflammation. The pathologic response to treatment is determined by the amount of residual viable carcinoma in relation to areas of fibrosis or fibroinflammation within the gross lesion (Fig. 4.13). This relationship can be expressed as the inverse percentage of a favorable treatment response. Thus, a 100% treatment response indicates fibrosis or fibroinflammation within an entire gross lesion without microscopic evidence of carcinoma, while a 0% response represents an entirely viable tumor in the absence of any fibrosis or fibroinflammation. The presence of viable tumor cells suggests incomplete response. Acellular mucin is regarded as a form of positive treatment response, not as viable tumor. The pathologic stage of the residual carcinoma is based on the deepest focus of viable malignant epithelium of the gastric wall. Positive lymph nodes are defined as having at least one focus of viable tumor cells in lymph nodes . As an alternative, 3 category systems also provide good interobserver reproducibility (Table 4.4) .
Fig. 4.13. Pathology assessment of gastric carcinoma post neoadjuvant therapy. a Gastric mucosa with surface ulceration and fibrin deposition (Marked by *) with clusters of residual carcinoma (arrow). b) Although the carcinoma is mostly viable (arrow), the treatment associated changes are apparent which include inflammation, fibrosis, and dystrophic calcification (dark spots). c) Moderate treatment effect with residual carcinoma preset as incomplete glands, small clusters, and individual cells. d) Marked treatment response with near complete tumor regressions; the residual tumor cells are present as rare single cells (arrows)
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