The `data_mutations_extended.txt` file (genie version 15.0) contains four entries where the reference allele and the tumor allele are identical. Such mutations are nonetheless reported as missense mutations in the `Variant_Classification` column: ``` Hugo_Symbol Chromosome Start_Position End_Position Reference_Allele Tumor_Seq_Allele2 Variant_Classification 0 BCL2 18 60985749 60985751 AGG AGG Missense_Mutation 1 BCL2 18 60985749 60985751 AGG AGG Missense_Mutation 2 TERT 5 1295250 1295253 GAGG GAGG Missense_Mutation 3 INPP4B 4 143352409 143352411 CCA CCA Missense_Mutation ```