Predictive value of tumor growth rate during previous treatment for tumor response to regorafenib (REGO) and trifluridine/tipiracil (TFTD) in metastatic colorectal cancer (mCRC).

Abstract

766 Background: Although REGO and TFTD have been recognized as standard salvage treatments for patients (pts) with refractory mCRC, it is still unclear which drug should be used first. Tumor growth rate (TGR) during the pre-treatment period is associated with survival in lung and laryngeal cancer treated with chemoradiotherapy. However, little is known about the association between TGR during the pre-treatment period and tumor response to REGO and TFTD. Methods: We retrospectively analyzed the data of consecutive mCRC pts who were treated with REGO or TFTD at three institutions. We classified pts into slow-growing (SG) or rapid-growing (RG) groups according to TGR, and appearance of new lesions (NL+) or their absence (NL–) during the pre-treatment period. TGR was calculated as follows: TGR = (D1 − D0)/100D0 (CT1 − CT0), where CT1 is the date of computed tomography (CT) at progressive disease, CT0 is the date of CT before CT1, and Dn is the sum of target lesion diameters at CTn (according to RECIST version 1.1). SG was defined as NL– with a low TGR ( < 0.33), and RG was defined as NL− with a high TGR (≥0.33) or NL+, irrespective of TGR. Results: A total of 244 pts (RG/SG: 133/111, REGO/TFTD: 132/112) were eligible. The proportion of RG pts with a long duration from first-line chemotherapy and SG pts with elevated ALP was higher in the REGO group, while the proportion of SG pts with poor PS was higher in the TFTD group. The disease control rate (DCR) was similar in both groups (REGO 29% vs TFTD 23%, p = 0.556) among RG pts, while the DCR of TFTD was significantly better than REGO in SG pts In a multivariate analysis of predictive factors for DCR, drug selection was an independent factor for DCR in SG pts (odds ratio 3.51; 95% CI 1.33-9.27; p = 0.011). In RG group, DCRs of NL+ pts were worse than that of NL- pts (16% vs 36% in REGO group, p = 0.109; 9% vs. 31% in TFTD group, 0.108). Conclusions: TGR during the pre-treatment period would be helpful in selecting between REGO and TFTD, especially for pts with slow-growing tumors. Pts with appearance of new lesions may not benefit from either REGO or TFTD as salvage treatment.