Post-transcriptional modifications, such as 5′ end capping, 3′ end polyadenylation and splicing, are necessary for the precise regulation of gene expression and transcriptome integrity. Therefore, it is not surprising that abnormalities of these post-transcriptional modifications prompt numerous diseases, including cancer. In fact, many studies revealed that misregulation of mRNA processing, especially splicing, are observed in a variety of cancer cells. In this review we describe how changes within RNA splicing regulatory elements or mutations in the processing factors alter the expression of tumor suppressors or oncogenes with pathological consequences. In addition, we show how several small molecules that bind to spliceosomal components and splicing regulators inhibit or modulate splicing activity. These compounds have anticancer activity and further development of small molecule modulators has potential in next generation cancer therapy.