Next, to investigate somatic genetic alterations of TCF4, its coding sequence and splice sites were sequenced in five of the above post-therapy samples with cancer cell content >70%; whilst many low-frequency mutations (allele frequency <10%) might appear post-therapy, one case with relapse after 139 months revealed a de novo intronic mutation that may affect TCF4 splicing regulation (c.717+23A>G; Fig. 5B and Table S7). This evidence concerns the gene TCF4 and cancer.