Value of Fine Needle Aspiration Biopsy in Toxic Thyroid Adenoma Nasr, I 1. Nagy, A2. Ali, I 3. Elsebaaie, A 4 1Oncology and Nuclear Medicine Department, Faculty of Medicine, Zagazig University. 2Nuclear Medicine Department, Al-maadi Military Hospital, Military Medical Academy. 3Radiology Department, Faculty of Medicine , Zagazig University, 4Pathology Department, International Medical Center, Military Medical Academy. Egyptian J. Nucl. Med., Vol. 17, No. 2, December 2018 (In press) ABSTRACT Background: The co-existence of thyroid cancer (TC) and hyperthyroidism (HT) cause serious diagnostic, therapeutic and prognostic difficulties Fine-needle aspiration biopsy (FNAB) is considered as essential step in the checkup of the thyroid nodule. Aim of the work. Assessment of the clinical value of FNAB and to determine frequency of thyroid cancer in patients with autonomous toxic thyroid adenoma, before radioactive iodine therapy. Methodology: All patients underwent clinical examination, thyroid hormonal profile analysis, neck ultrasound, Tc-99 thyroid scan and Fine Needle Aspiration Biopsy (FNAB). Twelve Patients with positive, suspicious or non-diagnostic FNAB results underwent thyroidectomy and histopathological analysis. Results: This study included forty one patients, 23 females (56.1%) and 18 males (43.9%) with mean age 39.8 (±9.3) years. All patients have elevated T3, T4 and suppressed TSH. All patients underwent FNAB; 29 patients (70.7%) were negative, two patients (4.9%) had TC, one patient (2.4%) was suspicious and 9 patients (22%) were non-diagnostic. Twelve patients with positive, suspicious or non-diagnostic FNAB results underwent thyroidecetomy followed by histopathological examination of the surgical specimens that confirmed features of TC in two patients with positive FNAB and one patient with suspicious FNAB, in addition to another one patient with non-diagnostic FNAB. Thyroid cancer was found on 4 patients (9.76%), three patients had papillary thyroid cancer and the fourth had follicular form proved by surgery. Conclusion: Addition of FNAB to work up list of patients with autonomous toxic thyroid adenoma prior to radioactive iodine therapy has added value in detection of malignancy. However surgery is recommended to confirm or exclude malignancy in patients with suspicious or non-diagnostic FNAB results. Keywords; Autonomous toxic adenoma; thyroid cancer; fine needle aspiration biopsy.