SMAD4 and neoplasm: Overall, the copy number profiles from matched tissue and ctDNA samples conformed closely with each other, even for chromosomes not covered by SNPs, as demonstrated for patient L16 in Fig. 4C. For instance, an amplification including KRAS on chromosome 12 and homozygous losses of regions including CDKN2A and SMAD4 on chromosome 9 and 18, respectively, were seen in both the diagnostic tumor biopsy and the BL plasma sample.