Problems of Thyroid Ultrasound Screening–Based on the Results of Thyroid Screening Conducted at Our Facility 25 Years Ago in Japan

Abstract

Surgical cases of papillary thyroid cancer have increased in many countries recently. The main factor is that the ultrasound examination device is widely used. Improved image quality is also a factor. We present the results of thyroid cancer screening through ultrasound examinations performed 25 years ago and mention the problem of over-diagnosis in thyroid cancer screening. From 1990 to 1995, we presented the results of our ultrasound screening for thyroid cancer in Kagawa Prefecture, Japan (1 million people). The subjects were 11,189 women with no neck symptoms. They were examined using a surface ultrasonic apparatus. After detecting abnormalities, fine needle aspiration cytology was carried out. If the patient were diagnosed with cancer, a lobectomy was performed with a side neck lymph node dissection. 140 cases of thyroid cancer were detected in this screening. The histological type of all detected cancer was papillary carcinoma. The detection rate of tumors with diameters of 3mm or more was 3.6%; 10mm or more was 0.88%; 15mm in the tumor diameter was 0.27%. Lymph node metastasis was observed 33% in tumors sized 3∼9mm, 56% in tumors sized 10∼14mm, and 94% in tumors sized 15mm or more.If we enforce the thyroid cancer screening by ultrasound examination, the detection of thyroid cancer in 3mm or more is 3600 per 100,000 women, the detection of 10mm or more is 880 per 100,000 women. But the annual number of suffering from thyroid cancer in Japan is approximately only 7 per 100,000 women. The deviation between the two is very large. We inferred that small papillary thyroid cancer is passed without problems accompanied by lymph node metastasis. For thyroid cancer screening using ultrasound, the problem of over-diagnosis is raised. The detection of thyroid cancer through aggressive use of ultrasound is not recommended. Surgical indications of subclinical thyroid cancer should be determined with restraint. Asymptomatic small papillary carcinoma should be regarded as innocuous.