Volume corrected mitotic index (M/V-INDEX). The standard of mitotic activity in neoplasms.

Estimation of mitotic activity by counting the number of mitotic figures per high power fields is subject to many sources of error. The microscope fields vary in size in different microscopes, which makes comparisons arbitrary. Also the areas covered by neoplastic and non-neoplastic tissue in the microscope image vary in different tumors. We found that each microscope could easily be characterized in terms of the size of the microscope field at 40x objective magnification (usually at ocular magnification of 10x). We also found that the number of mitotic figures can be related to the area covered by neoplastic tissue in the microscope field. The resulting index, the volume corrected mitotic index (M/V-index) will express the mitotic activity as the number of mitotic figures per square millimeter of neoplastic tissue in the microscope fields. The M/V-index will not be subject to the variation in volume fractions of neoplastic tissue between different neoplasms. With the M/V-index the mitotic activity as measured in different microscopes can be compared reliably. The value of the method is demonstrated in a series of ovarian tumors.