CONTEXT: Phyllodes tumors of the breast are uncommon, comprising 0.3% to 0.9% of female primary breast tumors. Owing in part to their rarity, definitive, objective, reproducible morphologic criteria that reliably distinguish benign from low-grade malignant or malignant phyllodes tumors have yet to be established. OBJECTIVE: To use image analysis to quantitate and compare morphologic features of different groups of fibroepithelial tumors (FETs) of the breast. DESIGN: Hematoxylin-eosin-stained sections of 41 FETs previously identified as fibroadenoma, benign phyllodes, low-grade malignant phyllodes, or high-grade malignant phyllodes were blinded and studied using a Leica DMRA2 microscope and OpenLab Image Analysis software. Features measured included mitotic rate per 10 high-power fields, stromal cellularity, nuclear size, stromal overgrowth, and the largest and smallest stromal-epithelial surface area ratios. Epithelial appearance was measured on a semiquantitative basis. Features of each case including tumor size, margin status, and the presence of necrosis or heterologous elements were also considered; these data were retrieved from surgical pathology reports. RESULTS: Quantitative measures of stromal cellularity, stromal-epithelial ratio, mitotic rate, stromal overgrowth, and mean nuclear diameter were developed and found to stratify a population of FETs by the current classification system of fibroadenoma, benign, and low-grade or high-grade malignant phyllodes tumor. CONCLUSIONS: Quantitative morphologic features of FETs can be used to stratify these tumors by subtype. Use of these quantitative criteria could reduce interrater variability in histologically identifying FETs by subclass.
CONTEXT: Phyllodestumors of the breast are uncommon, comprising 0.3% to 0.9% of female primary breast tumors. Owing in part to their rarity, definitive, objective, reproducible morphologic criteria that reliably distinguish benign from low-grade malignant or malignant phyllodestumors have yet to be established. OBJECTIVE: To use image analysis to quantitate and compare morphologic features of different groups of fibroepithelial tumors (FETs) of the breast. DESIGN:Hematoxylin-eosin-stained sections of 41 FETs previously identified as fibroadenoma, benign phyllodes, low-grade malignant phyllodes, or high-grade malignant phyllodes were blinded and studied using a Leica DMRA2 microscope and OpenLab Image Analysis software. Features measured included mitotic rate per 10 high-power fields, stromal cellularity, nuclear size, stromal overgrowth, and the largest and smallest stromal-epithelial surface area ratios. Epithelial appearance was measured on a semiquantitative basis. Features of each case including tumor size, margin status, and the presence of necrosis or heterologous elements were also considered; these data were retrieved from surgical pathology reports. RESULTS: Quantitative measures of stromal cellularity, stromal-epithelial ratio, mitotic rate, stromal overgrowth, and mean nuclear diameter were developed and found to stratify a population of FETs by the current classification system of fibroadenoma, benign, and low-grade or high-grade malignant phyllodestumor. CONCLUSIONS: Quantitative morphologic features of FETs can be used to stratify these tumors by subtype. Use of these quantitative criteria could reduce interrater variability in histologically identifying FETs by subclass.