TYMS and mucositis: We observed lower frequencies of severe mucositis only in patients who carried TS 2R/2R, MTHFR CT/TT, and MTRR AA genotypes and received HD-MTX together with ID-ARA-C; however, in our clinic we have not used ARA-C since 2003 because research has indicated that this treatment has no effect on relapse rate [40].