Pathologic response to preoperative chemotherapy in colorectal liver metastases: fibrosis, not necrosis, predicts outcome.

BACKGROUND: Pathologic response to preoperative chemotherapy for colorectal liver metastases (CLM) is associated with survival after hepatectomy. Histologically, dominant response patterns include fibrosis, necrosis and/or acellular mucin, but some of these changes can appear without previous chemotherapy and their individual correlation with outcome is unknown.
METHODS: Pathology slides from patients who underwent CLM resection (irrespective of preoperative chemotherapy status) were rereviewed by a blinded pathologist. Pathologic response was recorded as the summation of percentage necrosis, fibrosis and acellular mucin. Associations between pathologic response, its components, preoperative chemotherapy, and survival were analyzed.
RESULTS: Pathology slides were rereviewed in 366 patients undergoing CLM resection from 2003 to 2007. Preoperative chemotherapy was administered in 249 (68 %) patients, who, when compared to no preoperative chemotherapy patients, had higher rates of overall pathologic response (57 vs. 46 %, P < .01), fibrosis (21 vs. 12 %, P < .01) and acellular mucin (6 vs. 3 %, P = .05) but similar rates of necrosis (30 vs. 31 %, P = .30). In patients receiving preoperative chemotherapy, overall pathologic response ≥ 75 % (5 year, 83 vs. 47 %, P < .01) and fibrosis ≥ 40 % (5 year, 87 vs. 51 %, P < .01) independently correlated with disease-specific survival after hepatectomy. Preoperative hepatic artery infusion chemotherapy (P = .04) and bevacizumab (P = .05) were marginally associated with overall pathologic response and fibrosis, respectively.
CONCLUSIONS: Fibrosis is the predominant chemotherapy-related pathologic alteration driving the association of treatment response with survival after CLM resection. Necrosis in CLM is not related to chemotherapy or outcome.