Impact of tumour growth rate during preceding treatment on tumour response to regorafenib or trifluridine/tipiracil in refractory metastatic colorectal cancer

Background Although regorafenib (REG) and trifluridine/tipiracil (FTD/TPI) have been recognised as standard treatments in metastatic colorectal cancer (mCRC), the best option remains unclear. Pretreatment tumour growth rate (TGR) is associated with radiotherapeutic efficacy in laryngeal cancer. However, no reports are available on the association between TGR during preceding treatment and the efficacy of REG or FTD/TPI. Patients and methods We retrospectively analysed the data of consecutive mCRC patients treated with REG or FTD/TPI and classified them into slow-growing or rapid-growing (SG or RG) groups according to TGR and emergence of new lesion (NL+) or their absence (NL-) during preceding treatment period [SG: NL- with low TGR (<0.33%/day); RG: NL+ or high TGR (>= 0.33%/day)]. Results A total of 244 patients (RG/SG, 133/111; REG/FTD/TPI, 132/112) were eligible. The RG proportion with a long duration from first-line chemotherapy and the SG proportion with elevated alkaline phosphatase were higher in REG, whereas the SG proportion with performance status 2 was higher in FTD/TPI. The disease control rates (DCRs) were similar between REG and FTD/TPI (24%/30%; OR: 0.74; p=0.44; adjusted OR: 0.73; p=0.47) in the RG, whereas the DCR was significantly higher for FTD/TPI than for REG (47%/26%; OR: 2.56; p=0.029; adjusted OR: 3.38; p=0.01) in the SG. Conclusions TGR and NL during preceding treatment may be helpful for drug selection in refractory mCRC patients to be treated with REG or FTD/TPI. However, further studies are needed to confirm the value of TGR for drug selection.