Expression of mitoses per thousand cells and cell density in breast carcinomas: a proposal.

A method of standardizing mitotic counts is described. This provisional approach, which expresses mitoses as a percentage of breast cancer cells present, holds the promise of facilitating interlaboratory agreement as well as providing a measure of tumor cellularity, probably an independent prognostic indicator in its own right. We suggest that this approach or one similar to it will maximize the evaluation and quantitation of proliferative activity from routinely available histologic material. Furthermore, the method is accomplished with little added effort beyond the customary histologic evaluation.