There are a number of different types of tumors that are considered indeterminate: follicular neoplasm, Hurthle cell neoplasm, and atypical lesion. The word neoplasm means abnormal growth and it can be either benign or malignant (cancer). An indeterminate lesion means that the cells do not look normal, but that in order to make a diagnosis of cancer the whole nodule has to be examined under the microscope to see if there is invasion or growth outside of the nodule. This can only be done by removing part or all of the thyroid. In general, there is a roughly 20% chance of having a thyroid cancer with indeterminate lesions.