Our preliminary data indicate that the formation of micronuclei (MN) in treated tumor cells is a predictive variable for tumor response to treatment. In a pilot study involving four patients who received both radiation therapy and hyperthermia, fine needle aspirate (FNA) samples were taken and analyzed before therapy, and after each 1000 centigray (cGy) up to 3000 cGy. The results indicate a correlation between increasing formation of micronuclei and decreasing tumor volume. All of the patients in this Study have had their tumors under control for at least one year. Our preliminary data demonstrated that a high level of micronuclei in tumor cells correlates with favorable response of the tumor to treatment with radiation and heat. The assay is easy to perform and FNA biopsy could be done in the clinic with minimal discomfort to the patient.