Objective: CD117 and CD34 are markers that have both been implied in cancer progression in adult breast lesions. This study was conducted in order to create a retrospective documentation and to analyze the expression patterns of these markers on childhood benign lesions along with a comparison with adult breast lesions’ staining patterns.

Material and Method: Nine fibroadenomas, 2 tubular adenomas, 1 mammary hamartoma, 2 gynecomastias, 1 benign phyllodes tumor were retrieved from pathology archives of two reference centers between 2005-2010.

Results: CD117 staining was identified in the epithelium of all cases in fibroadenoma/tubular adenoma group and focally positive in 1 mammary hamartoma, 2 gynecomastias, and 1 benign phyllodes tumor. CD117 staining was detected in the stroma of 8 cases. Three fibroadenomas, 1 mammary hamartoma, 2 gynecomastias and 1 benign phyllodes tumor lacked stromal labelling for this marker. All cases were strongly and diffusely positive for CD34 except the benign phyllodes tumor case. This case presented marked loss of stromal CD34 staining when compared to the surrounding stroma. Additionally, pseudoangiomatous stromal hyperplasia was noted in 2 gynecomastias and in the peritumoral stroma of benign phyllodes tumor case.

Conclusion: Our study demonstrated that fibroadenoma was the most commonly encountered breast lesion in childhood and that adolescent fibroadenomas showed similar staining patterns for CD117 and CD34 as for adult counterparts. On the other hand, different expression patterns of CD117 and CD34 between adenoma group and the gynecomastias and benign phyllodes tumor group may implicate different mechanisms of development and tumorigenesis among these groups.