We compared the preplanned histopathological responses of resected liver metastases from patients who received modified FOLFOX6 plus bevacizumab or modified FOLFOX6 plus cetuximab for liver-limited colorectal metastases in the ATOM trial. Fibrosis and viable tumor cells in tumor regression grade (TRG), infarct-like necrosis in modified TRG (mTRG), and dangerous halo (DH) were assessed. Fifty-five patients (28 and 27 patients in the bevacizumab and cetuximab arms, respectively) were divided into the low (viable tumor cells ≤ 50%) and high (>50%) TRG or mTRG groups. DH was characterized as absent/rare or focal/diffuse. Compared to the bevacizumab arm, the cetuximab arm was more effective, with respect to low TRG (13 vs. 23 patients) and absent/rare DH (14 vs. 19 patients), respectively. Low mTRG was similarly observed in both arms. Low TRG/mTRG and absent/rare DH showed better relapse-free survival (RFS) than high TRG/mTRG and focal/diffuse DH. In the bevacizumab arm, a significant difference in RFS existed between the low and high TRG groups, while in the cetuximab arm, for TRG, mTRG, and DH, the low and absent/rare groups demonstrated significantly longer RFS than the high and focal/diffuse groups, respectively. TRG could estimate RFS in patients who underwent liver metastasectomy after bevacizumab or cetuximab chemotherapy.
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