Tumor thickness at the tumor-normal interface: A novel pathologic indicator of chemotherapy response in hepatic colorectal metastases

Background: Progress in the treatment of hepatic colorectal metastases (HCRM) demands pathologic indicators of therapy response. We observed that a majority of residual tumor cells are seen at the tumor-normal interface (TNI) in resected HCRM specimens and hypothesized that tumor thickness at the TNI correlates with radiologic and pathologic response and recurrence-free survival (RFS). Design: This study included 103 patients with HCRM resected after preoperative chemotherapy with or without bevacizumab. Imaging response was assessed by response evaluation criteria in solid tumors (RECIST) and recently described CT morphology criteria by Chun et al. The pathologic response was categorized as complete (no tumor cells), major (<50% residual tumor cells), or minor (≥50% residual tumor cells). The maximum thickness of uninterrupted layers of tumor cells was measured perpendicular to the TNI by 2 pathologists independently, followed by consensus review for discrepant cases. For specimens containing >1 tumor, the average tumor thickness at the TNI was used. Results: Sixty-five patients received oxaliplatin-based chemotherapy, 38 received irinotecan-based chemotherapy, and 75 received concurrent bevacizumab. A complete pathologic response was seen in 9 patients, a major response in 44, and a minor response in 50. Median tumor thickness at the TNI was 2.8mm (interquartile range, 0.5 to 6mm). Tumor thickness correlated better with radiologic response as determined by Chun et al (P<0.0001) than by RECIST criteria (Spearman r=0.35, P<0.001). Tumor thickness correlated with pathologic response (Spearman r=0.80, P<0.0001). Greater thickness predicted shorter recurrence-free survival, and this correlation remained in multivariate analysis (P=0.015). Tumor thickness was smaller in patients treated with bevacizumab than in patients not given bevacizumab (P=0.03). Conclusions: Tumor thickness measured at the TNI is potentially a new prognostic factor for therapy response and survival outcome in patients with resected HCRM.