Mammary
phyllodes tumors are uncommon stromal
neoplasms, and are divided into benign, borderline and malignant groups basing on histologic criteria. While benign
phyllodes tumors may recur, borderline
phyllodes tumors show higher propensity to recur locally and rarely metastasize, and malignant
phyllodes tumors show even higher chances of local recurrences or distant
metastases. c-kit is a proto-oncogene that encodes a
tyrosine kinase receptor (CD117) and is a marker for
gastrointestinal stromal tumors (GIST). With the advent of therapeutic agent targeted at this receptor for GIST, we investigated 179
phyllodes tumors (101 benign, 50 borderline, 28 malignant) for c-kit expression using immunohistochemistry. The staining was compared to the degree of
malignancy, and to the degree of stromal cellularity, mitotic activity, nuclear pleomorphism and stromal overgrowth. The overall positive rate for c-kit was 29% (52/179) and 17% (17/101), 24% (12/50) and 46% (13/28), respectively, for benign, borderline malignant and frank malignant phyllodes and the differences between all categories were significant (chi2=13.844, P=0.001). In mammary
phyllodes tumors, there was increasing c-kit expression with increasing degree of
malignancy, up to 46% in malignant cases. This provides strong evidence that
c-kit receptor mediated
tyrosine kinase involvement in the pathogenesis of
phyllodes tumors, and the therapeutic agent,
STI571,
Glivec, may be a potentially useful
drug for its management.