RET proto-oncogene mutation in a mixed medullary-follicular thyroid carcinoma

Selpercatinib for treating recurrent mixed medullary and follicular cell-derived thyroid carcinoma: a case report

BACKGROUND

Mixed medullary and follicular cell-derived thyroid carcinoma (MMFCC) is characterized by the coexistence of follicular and C cell-derived tumour cell populations within the same lesion. Due to its rarity, its etiology and clinical course remain unclear, and treatment for advanced or recurrent cases has not been established.

CASE PRESENTATION

We report a case of MMFCC treated with selpercatinib. The patient was a 69-year-old male presenting with tumors in the right thyroid lobe and in the upper mediastinum. Fine-needle aspiration (FNA) cytology of the right thyroid lobe tumor revealed a medullary carcinoma; germline RET mutations were not detected. After resection of the right thyroid lobe with central node dissection, rapid intraoperative diagnosis of the mediastinal mass confirmed malignancy, leading to total thyroidectomy with excision of the upper mediastinal tumor. Histologically, the tumor in the right thyroid lobe and the pretracheal lymph node revealed a mixture of medullary and follicular carcinoma components, diagnosed as MMFCC. The mediastinal lymph node exhibited only medullary carcinoma components. At 11 months postoperatively, computed tomography scans showed enlargement of the right supraclavicular and upper mediastinal lymph nodes. FNA cytology of the right supraclavicular lymph node suggested the recurrence of medullary thyroid carcinoma. The gene panel testing (The Oncomine Dx Target Test Multi-CDx system®, Thermo Fisher SCIENTIFIC) of metastatic lymph node revealed RET somatic mutation (M918T). Treatment with selpercatinib was initiated, and both the cervical and mediastinal lymph nodes showed a reduction in size.

CONCLUSIONS

We report a rare case of selpercatinib use for MMFCC. Since RET mutations may occur frequently in MMFCC, selpercatinib could be effective in treating MMFCC.

Multiple Endocrine Neoplasia Type 2B Associated Mixed Medullary and Follicular Thyroid Carcinoma in A Chinese Patient with RET M918T Germline Mutation

BACKGROUND

Mixed medullary and follicular thyroid carcinoma (MMFC) displays heterogeneous morphological components and immunophenotypical features intermingled within the same lesion, which is rare and most described in the sporadic form. We report herein a Chinese patient with multiple endocrine neoplasia type 2B (MEN2B) harboring germline RET M918T and associated MMFC.

METHODS

A case of a 39-year-old male patient with MEN2B presented palpable neck masses in both thyroid lobes (maximum sizes: left, 3.9 cm; right, 5.4 cm) and a definitive phenotype. Serum levels of calcitonin (Ctn; >2000pg/mL), carcinoembryonic antigen (CEA; 719.27ng/mL), and thyroglobulin (Tg; 98.54ng/mL) were high. Fine-needle aspiration cytology showed features positive for malignancy, suggesting the possibility of medullary thyroid carcinoma (MTC). Total thyroidectomy, along with extending bilateral neck lymph nodes dissection, and subsequently, genetics family screening were performed.

RESULTS

The histopathological examination yielded a diagnosis of MMFC that showed immunohistochemical characteristic patterns of the component of MTC positive for Ctn and CEA, chromogranin A, and the follicular carcinoma components were positive for Tg. Lymph node metastasis was observed showing medullary tumoral cells positive for Ctn and follicular-like structures lacking tumor cells positive for Tg staining (T4bN1bM0). Genetics screening confirmed RET M918T (c.2753T>C) mutation manifested in the patient but was not detected in other family members. Follow up showed that the serum Ctn, CEA and Tg levels respectively dropped to 54.38pg/ml, 4.16ng/mL and 0.04ng/mL 16 months after the surgery.

CONCLUSION

Particular and diverse patterns of MMFC should be recognized with immunostaining features. MMFC occurring in a patient with MEN2B harboring RET M918T may be unique biological behavior and the treatment is mostly radical surgery.

Mixed medullary-follicular carcinoma of the thyroid: diagnostic dilemmas in fine-needle aspiration cytology

Mixed medullary-follicular carcinoma (MMFC) of thyroid is an extremely rare tumor, characterized by coexistence of morphological and immunohistochemical features of both medullary carcinoma and follicular (or papillary) carcinoma. We herein present fine needle aspiration (FNA) findings of a histology-confirmed MMFC along with a review of literature. The patient was a 64-year-old woman who had a history of Hashimoto's thyroiditis and presented with enlargement of preexisting right thyroid nodule. An US-guided FNA of the thyroid nodule was performed and conventional smears were prepared. A cytologic diagnosis of "positive for malignancy, consistent with medullary thyroid carcinoma (MTC)" was rendered based on the presence of features characteristic for MTC, and the absence of components of follicular neoplasm (adenoma and carcinoma) or papillary carcinoma. However, microscopic examination of the follow-up total thyroidectomy specimen with the aid of immunocytochemical study detected minor portion of follicular carcinoma in addition to MTC. A histologic diagnosis of MMFC was then established. While specific identification of MMFC by FNA may be difficult, it should be emphasized that adequate sampling in conjunction with the proper immunostaining panel could have highlighted the different aspects of the mixed tumor.

Multiple endocrine neoplasia type 2

Multiple endocrine neoplasia type 2 (MEN 2) is an autosomal dominantly inherited tumor syndrome subclassified into three distinct syndromes: MEN 2A, MEN 2B and familial medullary thyroid carcinoma. In MEN 2 families, medullary thyroid carcinoma, pheochromocytomas and parathyroid adenomas occur with a variable frequency, also depending on the specific genetic defect involved. In 1993, the responsible MEN2 gene was identified. The genetic defect in these disorders involves the RET proto-oncogene on chromosome 10. The germline RET mutations result in a gain-of-function of the RET protein. Extensive studies on large families revealed that there is a strong genotype-phenotype correlation. In this review, guidelines for early diagnosis, including MEN2 gene mutation analysis, and treatment, including preventive surgery, periodic and clinical monitoring, have been formulated, enabling improvement of life expectancy and quality of life. Identification of the RET protein has also provided new insights into its function, and the specific pathways it effects involved in cell proliferation, migration, differentiation and survival. In the near future, identification of biological tumor markers will enable target-directed intervention and may prevent and/or delay progression of both primary and residual tumor growth.

A new germline point mutation in Ret exon 8 (cys515ser) in a family with medullary thyroid carcinoma

BACKGROUND

A novel Cys-Ser Ret germline point mutation in a 58-year-old woman with bilateral medullary thyroid carcinoma (MTC) prompted us to perform genetic analysis of the family and evaluate the biological consequences of such a mutation.

METHODS

Ret analysis by direct sequencing was performed in five family members. The biological activity and biochemical properties of the Ret- Cys515Ser mutant were analyzed in NIH-3T3 cells.

RESULTS

The proband's son, age 35, had the Ret- Cys515Ser mutation and the L769 CTT/CTG exon 13 polymorphic variant, which was also found in his father. Clinical evaluation of the son also revealed bilateral multifocal microscopic MTC and papillary thyroid carcinoma (PTC). In vitro and in vivo analysis indicated ligand-independent activation of the Ret-Cys515Ser mutant due to aberrant disulfide homodimerization, increased mitogenic activity, and ability to induce anchorage-independent growth in NIH-3T3 cells in comparison to wild-type Ret, suggesting a possible role of Cys515Ser in tumor development.

CONCLUSIONS

The Cys515Ser mutation adds to cysteine substitution groups that have been described in association with MTC. Our data also highlight the importance of performing a complete genetic analysis in patients who present with MTC.

Goblet cell carcinoids and other mixed neuroendocrine/nonneuroendocrine neoplasms

Within the spectrum of neuroendocrine tumors arising in different organs, intermediate and controversial entities exist displaying a coexistence of neuroendocrine and nonneuroendocrine cell populations, and that are grouped under terms such as "goblet cell carcinoid", "mixed endocrine-exocrine carcinoma", "combined carcinomas", or "adenocarcinoma with neuroendocrine differentiation". These tumors may display variable amounts of the two components, potentially ranging from 1 to 99%, and variable structural patterns, ranging from single scattered neuroendocrine cells to a well-defined neuroendocrine tumor cell component organized in typical organoid, trabecular, or solid growth patterns. Although variably included in the site-specific World Health Organization classification schemes, clear definitions and diagnostic features are still missing, as well as a definite knowledge of their biological properties and histogenesis. In the present report, the main characteristics of tumors showing mixed neuroendocrine and nonneuroendocrine features will be described, using morphological patterns and site of origin as schematic guidelines. Moreover, molecular and clinical aspects, which might help to understand their possible histogenesis and biological behavior, will be reviewed.

RET receptor signaling: dysfunction in thyroid cancer and Hirschsprung's disease

Gain-of-function mutations within the receptor tyrosine kinase gene RET cause inherited and non-inherited thyroid cancer. Somatic gene rearrangements of RET have been found in papillary thyroid carcinoma and germline point mutations in multiple endocrine neoplasia (MEN) types 2A and 2B and familial medullary thyroid carcinoma (FMTC). Conversely, loss-of-function mutations are responsible for the development of Hirschsprung's disease, a congenital malformation of the enteric nervous system. Comparison between normal RET signaling activated by the RET ligand glial cell line-derived neurotrophic factor (GDNF) and abnormal RET signaling caused by various mutations has led to a deeper understanding of disease mechanisms. The focus of the present review is on recent progress in the study of RET signaling dysfunction in human diseases.

RET tyrosine kinase signaling in development and cancer

The variety of diseases caused by mutations in RET receptor tyrosine kinase provides a classic example of phenotypic heterogeneity. Gain-of-function mutations of RET are associated with human cancer. Gene rearrangements juxtaposing the tyrosine kinase domain to heterologous gene partners have been found in sporadic papillary carcinomas of the thyroid (PTC). These rearrangements generate chimeric RET/PTC oncogenes. In the germline, point mutations of RET are responsible for multiple endocrine neoplasia type 2 (MEN 2A and 2B) and familial medullary thyroid carcinoma (FMTC). Both MEN 2 mutations and PTC gene rearrangements potentiate the intrinsic tyrosine kinase activity of RET and, ultimately, activate the RET downstream targets. Loss-of-function mutations of RET cause Hirschsprung's disease (HSCR) or colonic aganglionosis. A deeper understanding of the molecular signaling of normal versus abnormal RET activity in cancer will enable the development of potential new treatments for patients with sporadic and inherited thyroid cancer or MEN 2 syndrome. We now review the role and mechanisms of RET signaling in development and carcinogenesis.

The oncogenic activity of RET point mutants for follicular thyroid cells may account for the occurrence of papillary thyroid carcinoma in patients affected by familial medullary thyroid carcinoma

Activating germ-line point mutations in the RET receptor are responsible for multiple endocrine neoplasia type 2-associated medullary thyroid carcinoma (MTC), whereas somatic RET rearrangements are prevalent in papillary thyroid carcinomas (PTCs). Some rare kindreds, carrying point mutations in RET, are affected by both cancer types, suggesting that, under specific circumstances, point mutations in RET can drive the generation of PTC. Here we describe a family whose siblings, affected by both PTC and MTC, carried a germ-line point mutation in the RET extracellular domain, converting cysteine 634 into serine. We tested on thyroid follicular cells the transforming activity of RET(C634S), RET(K603Q), another mutant identified in a kindred with both PTC and MTC, RET(C634R) a commonly isolated allele in MEN2A, RET(M918T) responsible for MEN2B and also identified in kindreds with both PTC and MTC, and RET/PTC1 the rearranged oncogene that characterizes bona fide PTC in patients without MTC. We show that the various RET point mutants, but not wild-type RET, scored constitutive kinase activity and exerted mitogenic effects for thyroid PC Cl 3 cells, albeit at significantly lower levels compared to RET/PTC1. The low mitogenic activity of RET point mutants paralleled their reduced kinase activity compared to RET/PTC. Furthermore, RET point mutants maintained a protein domain, the intracellular juxtamembrane domain, that exerted negative effects on the mitogenic activity. In conclusion, RET point mutants can behave as dominant oncogenes for thyroid follicular cells. Their transforming activity, however, is rather modest, providing a possible explanation for the rare association of MTC with PTC.

Mixed follicular-medullary thyroid carcinoma: A case report

We report on a 35-yr-old woman presenting with a single thyroid nodule. Fine-needle aspiration (FNA) of the nodule was reported to contain both follicular and parafollicular cells. The biphasic nature of the tumor was highlighted on immunohistochemical investigation of the cellblock. Positive staining for thyroglobulin was limited to the follicular structures and the dense areas stained positive for calcitonin. The serum calcitonin level was highly elevated. Surgery was recommended because of suspected malignancy. The patient underwent total thyroidectomy. The diagnosis of mixed medullary and follicular carcinoma of the thyroid was established by histological investigation using immunohistochemical staining for thyroglobulin, chromogranin, and calcitonin. The patient was well 1 yr after the operation. Repeated measurements of serum calcitonin levels were normal. Total body scan revealed no radioactive iodine uptake in the thyroid bed, bones, or lungs.

C-cell and thyroid epithelial tumours and altered follicular development in transgenic mice expressing the long isoform of MEN 2A RET

Gain-of-function mutations in the gene encoding the receptor tyrosine kinase RET have been identified as the aetiological factor for multiple endocrine neoplasia type 2A (MEN2A). MEN2A is a dominantly-inherited cancer predisposition syndrome characterized by medullary thyroid carcinoma, a tumour of the calcitonin-producing thyroid C-cells. There are three isoforms of RET: RET9, RET43 and RET51, and although in vitro evidence suggests they vary in cellular transformation activities, little is known about their function in tumorigenesis in vivo. To address this, we used RET51 cDNA to construct mice in which the most frequent MEN2A mutation, Cys-634-Arg, was expressed under the control of the human calcitonin promoter (CT-2A mice). These mice developed C-cell tumours resembling human MTC and follicular tumours resembling human papillary thyroid carcinoma (PTC) depending on the founder line examined. One founder line developed compound MTC/PTC at low frequency (8%) and pancreatic cystadenocarcinoma. CT-2A mice also displayed a developmental defect in thyroid follicular structure, in which much of the thyroid was occupied by large irregular cystic follicles thought to be derived from the ultimobranchial body, a developmental precursor of the thyroid gland. The CT-2A mice will provide a suitable model to further study the effects of the MEN 2A RET mutation in vivo.