CHICAGO — A high rate of malignancy was found in a retrospective review of incidentally discovered thyroid nodules among patients with a history of other cancers, Dr. Scott M. Wilhelm reported at the annual meeting of the Central Surgical Association.
Traditionally discovered palpable nodules reportedly have a 5% malignancy rate, but some studies have suggested that nonpalpable nodules found during other radiographic procedures carry malignancy rates ranging from 8% to 29%.
Office-based ultrasound confirmed the presence of a nodule 1 cm or more in diameter in 35 of 41 patients who were referred for evaluation after CT scans identified thyroid nodules, said Dr. Wilhelm, assistant professor, Case Western Reserve University, Cleveland.
Most (78%) of the patients were female. The primary site in 23 of the patients was gastrointestinal, including colon, pancreas, and small bowel, whereas the primary site was breast in 11 patients and prostate in 4. Three patients had lymphoma, and nine had various other tumors.
In some patients, there was more than one primary tumor, Dr. Wilhelm said.
The remaining six patients had nodules that were smaller than 1 cm or had no nodules, and were considered to represent false-positive CT scans.
Biopsy results were benign in 15 (42.8%) of the 35 patients, malignant in 2 (5.7%), indeterminate in 16 (45.7%), and nondiagnostic in 2 (5.7%). The malignancies were papillary thyroid cancers, whereas the indeterminate biopsies were classified as follicular neoplasms or suspicious, but not definitive, for papillary thyroid cancer.
A total of 20 patients had diagnoses that warranted surgical resection. One additional patient whose biopsy was benign was subsequently picked up on an OctreoScan study.
“At the time there was very little in the literature on this, so we offered her resection as well,” said Dr. Wilhelm.
Seventeen of the 21 patients underwent resection, with results including four papillary thyroid carcinomas, four micropapillary cancers ranging in size from 4 mm to 8 mm, and seven benign lesions.
Two thyroid metastases also were found, one from renal cell carcinoma and one from melanoma.
Three patients had a history of radiation exposure to the head and neck. In two of the three patients, the exposure had occurred 40 years earlier, during treatment for infantile thymus in one and for eczema in the other. Both patients had atypical biopsies and underwent surgery, but the pathologies were benign.
The third patient had been treated 10 years earlier for breast cancer, undergoing radiation therapy for a supraclavicular lymph node, and was found to have micropapillary thyroid cancer.
“The rate of malignancy in our incidental thyroid nodules was 24%, but we felt it appropriate to exclude the micropapillary cancers, so that left us with 15%, which is three times the rate of malignancy seen in traditionally discovered palpable nodules,” Dr. Wilhelm said at the meeting.
These microscopic foci are very common but pose little risk to patients. In autopsy studies that include these, up to 30% of the population will be found to have nodules, which is why they were excluded in this study, he said.
Some earlier studies did not specify whether micropapillary cancers were included, which may account for rates that were even higher than in this investigation.
The overall increase in thyroid cancer in recent years may be contributing to the high rates of malignancy: American Cancer Society data from 2002 show an actual number of 22,700 new cases and an estimated number of 33,550 for 2007.
“In this study, we also may have selected out patients with unusual genetics,” Dr. Wilhelm said. “We had nine patients who had two primaries and one who had three primaries. Two of the thyroid cancers were in these patients, so one patient wound up with four tumors and one with three. Clearly, there is something different about them.”
The study findings also show that ultrasound was superior to CT in identifying nodules.
The correlation of thyroid nodule size that was seen on ultrasound with that found on pathology was excellent, and thyroid ultrasound should be considered essential if size is to be used as the criterion for determining which lesions to biopsy, Dr. Wilhelm emphasized.
An ultrasound shows a heterogenous thyroid nodule with very irregular borders. It turned out to be a papillary thyroid carcinoma on pathology. Courtesy Dr. Scott M. Wilhelm