Therefore, since JAK-STAT signalling can allow the transcription of genes involved in cell division, one potential effect of excessive JAK-STAT signalling is cancer formation. High levels of STAT activation have been associated with cancer; in particular, high amounts of STAT3 and STAT5 activation is mostly linked to more dangerous tumours.[59] For example, too much STAT3 activity has been associated with increasing the likelihood of melanoma (skin cancer) returning after treatment and abnormally high levels of STAT5 activity have been linked to a greater probability of patient death from prostate cancer.[60][59] Altered JAK-STAT signalling can also be involved in developing breast cancer.