A few studies have tried to evaluate the value of a second needle biopsy. Ultrasound criteria for malignancy have been described but are mostly unvalidated. Only a very small number of immunocytochemical studies using several antibodies have been reported, mostly dealing with series of less than 50 cases. The Bethesda State of Science Conference held in October 2007 (ahead on print, 2009) on fine-needle biopsy of the thyroid considered that no sufficiently robust studies of this technique had yet been carried out and that prospective studies were required.