The grading of Ewing's tumor, as of carcinoma and sarcoma, is exceedingly difficult. A number of factors make this so, among them, and most conspicuous in this study, is the total lack of differentiation of the tumor cell. This being true, the prognosis should always be guarded.

In order to discover, if possible, some criteria for estimating the degree of malignancy of Ewing's tumor, we have made a study of thirty cases from the standpoint of clinical findings, roentgenograms, therapeutic results, and microscopic features. The nuclear chromatin content, and the cell activity as measured by the number of mitotic figures per high-power field, seem to be the most significant of our findings. A classification of the tumors according to their chromatin content indicates that those containing a large number of chromatin knots are probably more malignant than those containing a lesser number.

In studying the cellular activity, the tumors were divided into three grades, according to the number of mitotic figures in a high-power field, as follows: Grade 1, one to five figures; Grade 2, six to ten figures; and Grade 3, eleven to fifteen figures. It would appear that a patient with a tumor having five or less mitotic figures (Grade 1) has approximately a 23-per-cent. chance to survive ten years and a 31-per-cent. chance to live five years, whereas, if the mitotic-figure count is eleven or above (Grade 3), he will probably live little over one year. None of the patients with tumors in Grade 2 of this series lived ten years, and three, or 33 per cent., lived over five years, one of whom is alive five years and six months after the onset of symptoms.

The roentgenographic evidence presented by these thirty cases indicates that the early stage, characterized by bone condensation, goes hand in hand with increased cellular activity, whereas late bone changes are usually accompanied by diminished cellular activity.

This group of cases is obviously too small from which to draw any definite conclusions regarding the gradation of Ewing's tumor. The authors propose, however, to continue their studies and trust that others will carry out similar investigations. Studies of large numbers of cases might throw more light upon this subject and lead to the discovery of a method of establishing a more accurate prognosis.