c-Kit expression and mutations in phyllodes tumors of the breast.

BACKGROUND: Phyllodes tumors (PTs) represent uncommon fibroepithelial lesions of the breast that express c-Kit and platelet-derived growth factor receptor-alpha, similar to gastrointestinal stromal tumors (GISTs). 'Activating' mutations in these genes underlie responsiveness of GISTs to imatinib. Standard treatment for breast PTs is wide local excision, with no role for targeted therapies. PATIENTS AND METHODS: c-Kit (CD117) expression was investigated by immunohistochemistry in 17 cases of breast PTs. Fourteen of these cases were also subjected to KIT mutation analysis by dideoxynucleotide sequencing.
RESULTS: Five out of 17 (29%) tumors showed weak stromal staining for CD117. No previously described 'activating' mutations were found in exons 9, 11, 13, or 17 of the KIT gene. A silent germline point mutation was found in exon 17 of one case.
CONCLUSION: These data do not suggest a pathogenetic role for KIT in breast PTs. Inhibition of c-Kit signaling is unlikely to be helpful in this condition.