Screening high-risk populations for thyroid cancer

Background. Children treated with radiotherapy to the neck or exposed to en vironmental radiation are at risk for developing thyroid cancer later in li fe. The best method for screening these high-risk patients is unclear. We s ystematically reviewed evidence on the accuracy of ultrasound and palpation to detect thyroid nodules and of fine needle aspiration (FNA), a confirmat ory test, to diagnose thyroid cancer. Procedure. We searched the MEDLINE da tabase for papers published since 1966, using the MeSH term thyroid neoplas ms and terms related to diagnostic test performance. To supplement our MEDL INE searches, we searched reference lists from recent reviews and articles recommended by thyroid cancer experts. We recorded the tests used, the gold standard determination of disease, the lest performance results, and the p resence of biases that could affect the reported results. We also abstracte d the number of patients who underwent surgery and the final diagnoses. We created two decision models: one for screening 10,000 medically irradiated patients, and one for screening 10,000 environmentally irradiated patients. Results, Using ultrasound as the gold standard determination of the presen ce of a nodule, the sensitivity of palpation for all sized nodules was 10-4 1 percent, indicating that a high proportion of nodules detected by ultraso und are too small to be palpated. Sensitivity of palpation increased with n odule size. The specificity of palpation ranged from 95 to 100%. In studies from referral centers, the reported sensitivity and specificity of FNA wer e 71-95 and 52-99%, respectively. However, most authors excluded the propor tion of patients (6-33%) who had inadequate or nondiagnostic FNA results wh en calculating sensitivity and specificity, even though 6-100% of these pat ients went on to have a diagnostic lobectomy. When each study was reanalyze d so that patients with nondiagnostic FNA results who went directly to surg ery were reclassified as positive tests, sensitivity increased slightly, bu t specificity dropped by 4-20 percentage points per study. The decision mod el for screening 10,000 medically irradiated patients revealed that if ultr asound were used as an initial screen,2,741 patients would have nodules at least 1 cm in size; assuming no patients with smaller nodules had surgery, 1,964 patients would have surgery; 275 patients would have a diagnosis of t hyroid cancer. Screening with ultrasound as an initial test would detect an additional 150 cases of thyroid cancer compared to those screened with pal pation. However, an additional 1,689 patients would have surgery for nonmal ignant nodules (compared to 480 patients with nonmalignant nodules screened with palpation). The yield for screening 10,000 environmentally irradiated patients was several times smaller than for screening 10,000 medically irr adiated patients. If 10,000 environmentally irradiated patients were screen ed initially with ultrasound, approximately 708 patients would have nodules at least 1 cm in size; 89 patients would have surgery; and 38 patients wou ld be diagnosed with thyroid cancer. Conclusions, Regardless of type of exp osure, testing initially with ultrasound detects several times more cases o f thyroid cancer than palpation. However, when ultrasound is the initial te st, many more patients also have surgery for nonmalignant nodules. Screenin g with palpation is not very reassuring, particularly to medically irradiat ed patients with negative rests, since almost half (46%) of these patients may have undetected nodules. Med. Pediatr. Oncol. 37:583-591, 2001. (C) 200 1 Wiley-Liss, Inc.