The prediction of outcome in the rare Hürthle cell tumor of the thyroid continues to present a problem to surgeons and pathologists. To better clarify the distinctions between benign and malignant tumors, we have measured DNA content by flow cytometry on isolated cell nuclei derived from archival paraffin-embedded tissue blocks of 125 Hürthle cell tumors operated from 1943 to 1985 at the Mayo Clinic, Rochester, Minnesota, U.S.A. Nuclear DNA ploidy patterns were divided into 3 groups. A DNA normal (diploid) pattern was found in 55% of 75 Hürthle cell adenomas and in 26% of 50 Hürthle cell cancers; a DNA tetraploid/polyploid pattern was found in 11% of benign, and 14% of malignant tumors. An abnormal DNA stemline was detected in 34% of benign and 60% of malignant tumors. Hürthle cell cancer was the histologic diagnosis in 24% of the DNA normal, 47% of the DNA tetraploid/polyploid, and 54% of the DNA aneuploid tumors. None of the patients with adenomas developed tumor recurrence. However, 20% of the euploid and 40% of the aneuploid tumors developed local or distant recurrences. Survival to thyroid cancer death was significantly correlated with DNA ploidy status (p=0.02) but did not correlate with either tumor size or histologic grade. To date, deaths from thyroid cancer have been confined to patients whose tumors were DNA aneuploid. We would conclude that determination of DNA ploidy status may not aid the surgical pathologist in the diagnosis of Hürthle cell cancer. However, when a patient's Hürthle cell cancer is DNA aneuploid, there is significant risk of death from thyroid cancer.
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