Follicular Variant of Papillary Thyroid Carcinoma Presenting as Toxic Nodule in an Adolescent: Coexistent Polymorphism of the TSHR and Gsα Genes

Introduction

T hyroid nodules are quite rare in the first two decades of life, but they are more often malignant than in adults, because approximately one-fourth of them are cancerous (1 –3). For this purpose, a careful diagnostic work-up, from the patient's history through a fine-needle aspiration biopsy (FNAB), is required (1,2). The finding of an autonomously functioning thyroid nodule (AFTN), although not common in this age group, is usually reassuring because it is assumed to be a benign adenoma. Consequently, FNAB is not recommended (4). Nevertheless, malignancy may be found in AFTNs with non-negligible frequency in both adults and children (5 –14).

The etiopathogenesis of functional hyperactivity (hyperthyroidism) in a malignant thyroid nodule is still unknown. Regarding thyroid autonomy, somatic mutations of the thyrotropin receptor (TSHR) gene have been reported in toxic adenomas and toxic multinodular goiters, with a frequency widely ranging from 8% to 82% of cases (15 –17). Activating mutations of the Gsα (GNAS1) gene were also reported in 3% to 38% of toxic nodules (18). Nevertheless, the percentage of TSHR and/or Gsα mutation negative clonal hot nodules is not negligible, suggesting alternative molecular aberrations leading to the development of toxic nodules (19). Germline, and therefore inheritable, TSHR gene mutations occur in familial and sporadic nonautoimmune hyperthyroidism (20,21). Somatic mutations of the TSHR gene have also been described in cases of hyperfunctioning carcinomas (12,13,22 –27), and there is evidence for a role of TSHR and/or Gsα mutations in thyroid tumorigenesis (28 –31).

Herein, we present a 15-year-old girl with a papillary thyroid carcinoma of 3.5 cm in diameter, which was functionally autonomous and scintigraphically hot. Molecular studies were performed to search for TSHR and/or Gsα, as well as for BRAF and RAS gene mutations.

Patient

A 15-year-old female patient was referred to our Endocrine Unit because of a painless mass in the right anterior side of the neck that had appeared a few months earlier. She had a family history of Hashimoto's thyroiditis (her father). Ultrasound (US) examination revealed a 25-mm isoechoic, nonhomogenous nodule, with regular margins, a peripheral halo, and a perinodular blood flow, in the lower portion of the right thyroid lobe. Serum TSH was 0.27 mU/L (normal range 0.27–4.2), free triiodothyronine (FT3) and free thyroxine (FT4) levels were within normal limits. Serum anti-thyroglobulin and anti-peroxidase antibodies, as well as anti-TSHR antibodies were undetectable. Radioactive iodine (¹³¹I) thyroid scintigraphy revealed an avid uptake of the tracer in the right lower lobe, with no uptake by the extra nodular tissue, consistently with an AFTN (Fig. 1a). Within 6 months, the clinical picture quickly evolved into overt hyperthyroidism. The girl returned complaining of fatigue, weight loss, and palpitations of one-month duration. Physical examination revealed warm and moist skin, tremors of the extremities, and tendon hyper-reflexia. The patient's weight was 42.5 kg, her blood pressure was 140/70 mmHg, and pulse rate 94/min. FT3 and FT4 were elevated (5.0 pg/mL, normal values 2–4.4; and 20.15 pg/mL, normal values 9–17; respectively), TSH suppressed (0.001 mU/L). Thyroid US—done by the same investigator at our University Hospital—revealed an increase in size of the right nodule (35 mm×30 mm×21 mm), that also displayed an intense intranodular blood flow by color doppler. The nodule was isoechoic, nonhomogenous, with regular margins and a peripheral halo; no microcalcifications were present. Treatment with methimazole (20 mg/day) was started with progressive attenuation of symptoms and signs of thyrotoxicosis and normalization of FT3 and FT4 values. As per appropriate guidelines (1,2,10,11), FNAB was not performed and the patient was referred to surgeons for the definitive cure of the AFTN. Pathological examination revealed a papillary carcinoma, follicular variant (Fig. 1b). Noteworthy, the whole nodule of 3.5 cm in maximum diameter consisted of well-differentiated cancerous tissue. The excised nodule was examined for activating mutations of TSHR, Gsα, H-RAS, N-RAS, K-RAS, and BRAF genes by direct sequencing (for methodological details, see Supplementary Data, available online at www.liebertpub.com/thy). No genetic alterations were found, except for two combined nonfunctioning variants: a single-nucleotide polymorphism (SNP) of the TSHR gene, in exon 7, at codon 187 (AAT→AAC, both encoding asparagine), and a SNP within exon 8 of the Gsα gene at codon 185 (ATC→ATT, both encoding isoleucine). The two SNPs were detected also in the germline DNA of our patient. Sequencing of germline DNA from her parents showed that her father was heterozygous for the TSHR SNP, her mother heterozygous for the Gsα SNP, and her brother wild type. We evaluated the genotype distribution of these SNPs in 100 healthy individuals from the same geographic area and we found that they are rare: 9% were heterozygous for the TSHR SNP, and 7% were heterozygous for the Gsα SNP. None harbored both SNPs, unlike our index patient.

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FIG. 1.

Radioactive iodine (¹³¹I) thyroid scan, demonstrating the avid uptake of the tracer by the nodule (large arrow) with exclusion of the extra-nodular tissue (a). The histologic picture revealed a papillary carcinoma, follicular variant (b: hematoxylin–eosin, magnification 150×). On hematoxylin–eosin stained slides, the neoplasm showed a quite diffuse follicular arrangement with a small quantity of colloid within follicular lumina; the nuclei of thyreocytes were crowded and overlapping with the characteristic pale nucleoplasm.

Discussion

This 15-year-old girl demonstrates that the finding of AFTN(s) does not rule out cancer. Unfortunately, distinction between benign and malignant disease is often difficult. In our case, there were no clues to suspect malignancy preoperatively. The clinical presentation was dominated by the classic signs and symptoms of hyperthyroidism, and US did not reveal any feature of suspected malignancy. The progressive growth of the nodule in few months and its intense internal vascularization could be attributed to its functional overactivity. Since hot nodules usually grow slowly, the rapid growth of the nodule in our patient could also be interpreted as a sign of malignancy, but the US finding of a solid isoechogenic lesion with regular margins and a peripheral halo, without suspicious regional lymph nodes accompanying the thyroid nodule, was reassuring. Moreover, the most common risk factors predisposing to childhood thyroid cancer (i.e., age <10 years, male sex, family history of thyroid cancer, prior exposure to radiation) (1) were absent. In previous reports, an incomplete suppression of radionuclide uptake in extra-nodular thyroid tissues has been emphasized as a risk factor of malignancy (the so-called nonclassic hot nodules) (1,11), but this was not the case for our patient. We also doubt that performing FNAB would have helped in the diagnosis, because the follicular variant of papillary thyroid cancer is often difficult to distinguish from a benign follicular adenoma or hyperplastic nodule, these being the cytological findings expected in the case of AFTNs. Thus, AFTNs, even if unusual, deserve careful evaluation in childhood and adolescence. Indeed, AFTNs in the younger age group seem to have a different biologic potential than in the older age group because of an earlier progression toward toxicity and a higher incidence of thyroid carcinoma. Furthermore, it remains a great challenge to differentiate between malignant and benign lesions preoperatively. For these reasons, surgery is proposed as the treatment of choice of AFTNs in childhood and adolescence, while ¹³¹I therapy is not advisable in this age group (1,10,11).

Concerning the association between TSHR or Gsα mutations and malignant hot thyroid nodules, there is a limited number of case reports in the literature (12,13,22 –27). In regard to young patients, a somatic activating TSHR mutation at codon 453 (T→C transition, leading to substitution of threonine for methionine), was identified in a hot thyroid nodule containing papillary thyroid cancer tissue in a 11-year-old girl with nonautoimmune hyperthyroidism (12). In our patient, molecular analysis for TSHR and/or Gsα activating mutations was negative. Nevertheless, we found two silent SNPs: in exon 7 of the TSHR gene (codon 187, AAT→AAC), and in exon 8 of the Gsα gene (codon 185, ATC→ATT). The same SNPs were identified in two family members: the father was heterozygous for the TSHR polymorphism but wild type for Gsα, while the mother was heterozygous for the Gsα polymorphism and wild type for the TSHR variant. Of interest, the TSHR SNP was found to be associated with familial nonautoimmune hyperthyroidism, as well as with AFTNs (32,33). To the best of our knowledge, no other data are available in the literature about the prevalence of each of the two SNPs in AFTNs as well as in the general population. Thus, the possible association between AFTNs and SNPs of the TSHR gene, as evidenced also by other reports from the literature, is still a matter of debate (33 –36).

In conclusion, the presence of a hot nodule cannot always rule out thyroid cancer, and warrants careful evaluation, especially in children and adolescents, so that malignancy is not overlooked.