A Study of On-treatment ctDNA Changes in Chemo-refractory Colorectal Cancer Patients

"For subjects receiving treatments with a 2- or 4-weekly schedule, samples for ctDNA testing will be collected at the following timepoints:~Blood :~* Before treatment start (day 1)~* 2 weeks after treatment start (day 15)~Plasma :~* Before the treatment start (day 1)~* 4 weeks after treatment start (day 29)~* 8 or 12 weeks after treatment start and every 8 or 12 weeks thereafter (i.e. at the same time of each imaging tumour assessment) until evidence of progressive disease by RECIST 1.1~For subjects receiving treatments with a 3-weekly schedule, samples for ctDNA testing will be collected at the following timepoints:~Blood :~* Before treatment start (day 1)~* 3 weeks after treatment start (day 22)~Plasma :~* Before treatment start (day 1)~* 6 weeks after treatment start (day 43)~* 8 or 12 weeks after treatment start and every 8 or 12 weeks thereafter (i.e. at the same time of each imaging tumour assessment) until evidence of progressive disease by RECIST 1.1"