A method for detecting a tandem duplication in an FLT3 gene of a sample, includes mapping reads corresponding to targeted regions of exons of the FLT3 gene to a reference sequence. A partially mapped read includes a mapped portion, a soft-clipped portion and a breakpoint. Analyzing the partially mapped reads intersecting a column of the pileup includes detecting a duplication in the soft-clipped portion by comparing the soft-clipped portion to the mapped portion adjacent to the breakpoint; determining an insert size of the duplication in the soft-clipped portion; and assigning the partially mapped read to a category based on the insert size. Categories correspond to insert sizes. The categories are filtered and converted into features corresponding to the column. The features corresponding to one or more columns representing a same insert are merged to determine a location and size of a tandem duplication.