Differential mRNA isoform expression has been observed in breast cancer and may occur through alternate promoter usage, alternate splicing, and alternate 3′UTR usage.56 Importantly, differential mRNA isoform expression has been identified and associated with distinct breast cancer subtypes.56 Specific to the NF1 gene, splice variation has also been described.57,58 Our data strongly extend these findings as we show that both mutation type (IF and PS) and splice variation lead to more aggressive disease. Here, NF1 is linked to breast cancer.