Preoperative chemotherapy in patients undergoing resection of colorectal liver metastases: Assessment of pattern of tumor response using CT registration imaging.

Abstract

252 Background: A significant radiologic response from preoperative chemotherapy may successfully convert some unresectable colorectal liver metastases (CRLM) to resectable disease. Understanding the pattern of tumor shrinkage in relation to the hepatic structures such as the liver capsule and vascular pedicles is important. We sought to determine the spatial relationship between individual liver metastases before and after chemotherapy, as well as to adjacent intrahepatic structures. Methods: Using nonrigid registration of temporally separated CT scans before and after preoperative chemotherapy, 42 CRLM were evaluated in 27 patients with radiologic partial response. The response pattern was determined by independent observers and scored as: (1) asymmetric toward the liver periphery, (2) asymmetric toward the liver center, and (3) symmetric response. In addition, the shrinking pattern was characterized in relation to the liver capsule and major vascular pedicles, as well as clinicopathologic features. Results: Among the tumors evaluated, 38/42 lesions (90%) responded asymmetrically, with only 10% undergoing a symmetric contraction. 43% shrank toward the periphery and 47% centrally. Tumors in proximity to the liver capsule were more likely to respond peripherally compared to deeper lesions (p=0.013). Unexpectedly, R1 resection was more common in tumors with peripherally directed response vs. those with central or symmetric response (p=0.027). In addition, tumors within 5 mm of a single major vascular pedicle were more likely to shrink toward (59%) and not away from the vessel. No difference in response pattern was observed in relation to tumor size, chemotherapy regimen, or presence of steatosis. Conclusions: Tumors were found to respond asymmetrically in the vast majority of cases, either toward or away from the liver center. In addition, tumors in proximity to major vascular pedicles less commonly move away from these structures. These findings may have important implications when planning curative-intent resection or anticipating the ability to convert patients to resectable disease using preoperative chemotherapy. No significant financial relationships to disclose.