There is no commonly accepted grading scheme for phyllodes tumors of the breast, which can range from relatively benign to aggressive tumors. Lester gives one method for grading these tumors.
Parameters:
(1) cellularity
(2) nuclear pleomorphism
(3) mitotic rate in 10 high power microscopic fields (HPF, using 40x objective)
(4) stromal overgrowth (areas with abundant stroma and no epithelial cells)
(5) borders/margins of the tumor
(6) heterologous elements
Histologic Feature
Low Grade
Intermediate ("Borderline")
High Grade
stromal cellularity
mild
moderate
marked
nuclear pleomorphism
minimal
moderate
marked
mitotic rate
present but low (0 to 1 in 10 HPF)
2 to 10 in 10 HPF
> 10 in 10 HPF
stromal overgrowth
absent or focal
often present
may be marked
borders
pushing, well-circumscribed
some infiltration
marked invasion
heterologous elements
benign, usually bone or fat
benign, usually bone or fat
malignant stromal elements
where:
• The data given by Lester used mitotic rate of 2-5 for intermediate and >= 6 for high grade. I have used the WHO criteria in the table above..
Limitations:
• Low grade tumors have been known to metastasize.
• High grade tumors have been cured by simple excision.
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