The characteristic properties of oxyphilic tumors are as follows:

1. Great proportion of follicular cells exhibit oxyphilic metaplasia.
2. The cells are arranged in small non-specific clusters and in micro- and normofollicles. The ratio of follicles to other type of cell groups is significantly less than in usual follicular tumors. There is a tendency of cells to dissociate from groups, and therefore the ratio of dispersed cells to cells within groups is significantly higher than in hyperplastic nodules exhibiting oxyphilic changes.
3. Relatively great proportion of cells contains prominent nucleoli.
4. The presence of grooves or inclusions has a significantly less specificity in the diagnosis of malignant form of oxyphilic tumors compared with tumors composed of non-metaplastic cells.