RET Proto-Oncogene Testing

Number: 0319


  1. Aetna considers tests for germline point mutations in the RET gene medically necessary for members who meet any of the following high-risk criteria:

    • Members who have first-degree blood relatives (ie, parent, full-sibling, child) with medullary thyroid carcinoma (MTC)Footnotes*; or
    • Members who have first- (i.e., parent, full-sibling, child) or second-degree (i.e., aunt, uncle, grandparent, grandchild, niece, nephew, half-sibling) blood relatives and germline RET mutations (Testing strategy: Test for specific familial mutation); or
    • Members with any of the followingFootnotes*: c-cell hyperplasia; endocrine tumors, two or more; Hirschsprung disease; MTC; paraganglioma; parathyroid carcinoma; or pheochromocytoma.

      Footnotes*Testing Strategy: Sequencing of the RET gene may be considered.  

  2. Aetna considers diagnostic testing for germline point mutations in the RET gene medically necessary for members with apparently sporadic medullary thyroid carcinoma.

  3. Aetna considers tests for germline point mutations in the RET gene experimental and investigational for all other indications (e.g., non-small cell lung cancer; not an all-inclusive list) because its effectiveness for indications other than the ones listed above has not been established.

See CPB 0140 - Genetic Testing for policy on genetic testing for non-member relatives of Aetna members.


Multiple endocrine neoplasia (MEN) is a rare heritable disorder that affects the endocrine system and consists of the development of tumors (neoplasia) in at least two endocrine glands, though tumors can also develop elsewhere. These tumors can be noncancerous (benign) or cancerous (malignant). There are three major types of MEN: type 1 (MEN1), type 2 (MEN2) and type 4 (MEN4).

MEN1 is characterized by tumors of the parathyroid glands, anterior pituitary and pancreatic islet cells and is caused by mutations in the MEN1 gene.

Medullary Thyroid Carcinoma (MTC) is a cancer of the thyroid gland that starts in cells that release calcitonin. MTC is a common characteristic among individuals with MEN2. Some individuals with MEN2 also have pheochromocytoma, a tumor of the adrenal gland which causes high blood pressure. MEN2 is divided into three subtypes: type 2A (MEN2A), type 2B (MEN2B) and familial medullary thyroid carcinoma (FMTC). MEN2 is caused by mutations in the RET gene.

MEN4 appears to have similar signs and symptoms to MEN1; however, it is caused by mutations in the CDKN1B gene.

Genetic testing for RET germline mutation has shown 100 % sensitivity and specificity for identifying those at risk for developing inherited medullary thyroid cancer (multiple endocrine neoplasia (MEN) 2A, MEN 2B, or familial medullary thyroid carcinoma (FMTC)).  Use of the genetic assay allows earlier and more definitive identification and clinical management of those with a familial risk for medullary thyroid cancer when compared to the existing standard of annual biochemical monitoring.

Medullary thyroid carcinoma is surgically curable if detected before it has spread to regional lymph nodes.  However, lymph node involvement at diagnosis may be found in up to 75 % of patients for whom a thyroid nodule is the first sign of disease.  Thus, there is an emphasis on early detection and intervention in families, which are affected by the familial cancer syndromes of MEN types 2A and 2B and FMTC, which account for 25 % of medullary thyroid cancer.

After genetic counseling, most family members who test positive undergo surgery to remove the thyroid gland.  First-degree relatives of those with MTC that appears to be sporadic in origin also undergo the biochemical test to verify that the patient's tumor is not caused by an inheritable form of this disease.

Fialkowski et al (2008) stated that multiple endocrine neoplasia type2A (MEN 2A) is a genetic syndrome manifesting as MTC, hyper-parathyroidism, and pheochromocytoma.  Multiple endocrine neoplasia 2A results from mutations in the RET proto-oncogene. Hirschsprung Disease (HD) is a congenital condition characterized by a blockage of the large intestine due to poor muscle movement in the bowel. HD is a rare manifestation of MEN 2A and has been described in known MEN 2A families.  These investigators described 2 MEN 2A families that were only identified after the diagnosis of HD.  Kindred 1: A boy presented in infancy with HD.  Genetic screening revealed a C609Y mutation, which is consistent with MEN 2A.  Evaluation of his sister, father, and grandmother revealed the same mutation.  All 3 had thyroidectomies demonstrating C-cell hyperplasia.  The grandmother had a microscopic focus of MTC.  Kindred 2: An infant boy and his sister were diagnosed with HD as neonates.  Genetic testing demonstrated a C620R gene mutation consistent with MEN 2A.  Total thyroidectomies revealed metastatic MTC in the father and C-cell hyperplasia in both children.  The authors concluded that HD can be the initial presentation of MEN 2A. They strongly recommend that genetic screening be performed in patients presenting with HD, looking for the known RET mutations associated with MEN 2A.  If a mutation consistent with MEN 2A is detected, genetic screening of all first-degree relatives in the kindred is recommended.

In a case report, Pandey et al (2011) emphasized that all patients with a history of HD should consider screening for RET mutations (it should be noted that RET mutations are the predominant but only one of a number of possible causes of HD), as there is a well-established association between HD and MEN 2A.  If present, this could facilitate early diagnosis of MEN 2A with resultant thyroidectomy prior to the onset of MTC or at least prior to the development of metastatic disease.

Vaclavikova et al (2012) noted that inactivating germline mutations in the RET proto-oncogene are the major genetic cause of HD.  In some cases, HD can be associated with MTC that is commonly caused by activating RET mutations.  These investigators performed retrospective and prospective genetic analyses of 157 patients with HD operated on between December 1979 and June 2011; DNA was isolated from peripheral leukocytes.  Patients with HD as well as family members were tested for RET mutations by direct sequencing and single-strand conformation polymorphism methods.  RET mutations were detected in 16 patients (10 %).  Association with MTC was found in 2 families, other 8 families had a mutation with potentially high- risk of MTC development and 4 novel mutations were detected.  Total colonic aganglionosis was noted to have a high mutation detection rate (40 %).  Three patients underwent total thyroidectomy (2 had clinical manifestation of MTC, 1 C-cell hyperplasia).  The authors concluded that these findings showed the benefit of systematic RET mutation screening in HD patients in order to identify the risk of MTC in the preclinical stage of the disease.  All patients should be tested for RET mutations at least in exon 10, and now additionally in exon 11 and 13, as well.

An UpToDate review on “Clinical manifestations and diagnosis of multiple endocrine neoplasia type 2” (Lips, 2013) states that “Hirschsprung disease (HD) is characterized by the absence of autonomic ganglion cells within the distal colonic parasympathetic plexus resulting in chronic obstruction and megacolon.  In humans, inactivating mutations of the RET proto-oncogene have been associated with HD.  HD is a heterogenic disorder, occurring both in a familial and in a sporadic form.  In about 50 percent of familial and 15 to 35 percent of sporadic HD patients, mutations in the RET gene are involved.  Most HD cases arise from loss of function mutations, RET haploinsufficiency, RET polymorphisms or haplotypes of the RET promotor region.  Hirschsprung disease (HD) was found in 50 percent of children in a family with a C620 mutation .... RET proto-oncogene testing in infants presenting with Hirschsprung disease is useful and may identify new multiple endocrine neoplasia 2A kindreds”.

An UpToDate review on “Medullary thyroid cancer: Clinical manifestations, diagnosis, and staging” (Tuttle, 2014) states that “In a patient with negative RET proto-oncogene testing and no family history of MEN2 syndrome, biochemical testing for coexisting tumors is typically not required”.

In summary, RET proto-oncogene tests can be used to identify familial disease-causing RET point mutations in members of families known to be affected by inherited MTC.  For members of families with defined RET point mutations, results of the RET proto-oncogene tests may be used to decide upon prophylactic thyroidectomy or continued monitoring is necessary.  RET proto-oncogene tests may also be used to distinguish sporadic tumors from familial cancers in patients with MTC but without a previous family history of this disease, and in their first-degree relatives if the patient is found to have a germline RET mutation.  Furthermore, RET proto-oncogene tests are also of clinical value for individuals with Hirschsprung disease.

Non-Small Cell Lung Cancer

Yoshida et al (2013) noted that recent discovery of ROS1 gene fusion in a subset of lung cancers has raised clinical interest, because ROS1 fusion-positive cancers are reportedly sensitive to kinase inhibitors.  To better understand these tumors, these researchers examined 799 surgically resected non-small cell lung cancers (NSCLCs) by reverse transcriptase polymerase chain reaction (PCR) and identified 15 tumors harboring ROS1 fusion transcripts (2.5 % of adenocarcinomas).  The most frequent fusion partner was CD74 followed by EZR.  The affected patients were often younger non-smoking female individuals, and they had overall survival (OS) rates similar to those of the ROS1 fusion-negative cancer patients.  All the ROS1 fusion-positive tumors were adenocarcinomas except 1, which was an adenosquamous carcinoma.  Histologic examination identified an at least focal presence of either solid growth with signet-ring cells or cribriform architecture with abundant extracellular mucus in 53 % of the cases.  These 2 patterns were reportedly also characteristic of anaplastic lymphoma kinase (ALK)-rearranged lung cancers, and these data suggested a phenotypic resemblance between the ROS1-rearranged and ALK-rearranged tumors.  All tumors except 1 were immune-reactive to thyroid transcription factor-1.  Fluorescence in-situ hybridization (FISH) using ROS1 break-apart probes revealed positive re-arrangement signals in 23 % to 93 % of the tumor cells in ROS1 fusion-positive cancers, which were readily distinguished using a 15 % cutoff value from 50 ROS1 fusion-negative tumors tested, which showed 0 % to 6 % re-arrangement signals.  However, this perfect test performance was achieved only when isolated 3' signals were included along with classic split signals in the definition of re-arrangement positivity.  Fluorescence in-situ hybridization signal patterns were unrelated to 5' fusion partner genes.  All ROS1 fusion-positive tumors lacked alteration of epidermal growth factor receptor (EGFR), KRAS, HER2, ALK, and RET genes.

Lira et al (2014) stated that approximately 7 % of NSCLCs harbor oncogenic fusions involving ALK, ROS1, and RET.  Although tumors harboring ALK fusions are highly sensitive to crizotinib, emerging pre-clinical and clinical data demonstrated that patients with ROS1 or RET fusions may also benefit from inhibitors targeting these kinases.  Using a transcript-based method, these investigators designed a combination of 3' over-expression and fusion-specific detection strategies to detect ALK, ROS1 and RET fusion transcripts in NSCLC tumors.  They validated the assay in 295 NSCLC specimens and showed that the assay is highly sensitive and specific.  ALK results were 100 % concordant with FISH (n = 52) and 97.8 % concordant with IHC (n = 179) [sensitivity, 96.8 % (95 % confidence interval [CI]: 91.0 % to 98.9 %); specificity, 98.8 % (95 % CI: 93.6 % to 99.8 %)].  For ROS1 and RET, these researchers also observed 100 % concordance with FISH (n = 46 and n = 15, respectively).  They identified 7 ROS1 and 14 RET fusion-positive tumors and confirmed the fusion status by RT-PCR and FISH.  One RET fusion involved a novel partner, cutlike homeobox 1 gene (CUX1), yielding an in-frame CUX1-RET fusion.  ROS1 and RET fusions were significantly enriched in tumors without KRAS/EGFR/ALK alterations.  ALK/ROS1/RET/EGFR/KRAS alterations were mutually exclusive.  The authors concluded that as a single-tube assay, this test showed promise as a more practical and cost-effective screening modality for detecting rare but targetable fusions in NSCLC.

Wijesinghe et al (2015) noted that ROS1 and RET gene fusions were recently discovered in NSCLC as potential therapeutic targets with small-molecule kinase inhibitors.  The conventional screening methods of these fusions are time-consuming and require samples of high quality and quantity.  These researchers described a novel and efficient method by coupling the power of multiplexing PCR and the sensitivity of mass spectrometry.  The multiplex mass spectrometry platform simultaneously tests samples for the expression of 9 ROS1 and 6 RET fusion genes.  The assay incorporated detection of wild-type exon junctions immediately up-stream and down-stream of the fusion junction to exclude false-negative results.  To flag false-positives, the system also comprised 2 independent assays for each fusion gene junction.  The characteristic mass spectrometric peaks of the gene fusions were obtained using engineered plasmid constructs.  Specific assays targeting the wild-type gene exon junctions were validated using complimentary DNA from lung tissue of healthy individuals.  The system was further validated using complimentary DNA derived from NSCLC cell lines that express endogenous fusion genes.  The expressed ROS1-SLC34A2 and CCDC6-RET gene fusions from the NSCLC cell lines HCC78 and LC-2/ad, respectively, were accurately detected by the novel assay.  The assay is extremely sensitive, capable of detecting an event in test specimens containing 0.5 % positive tumors.  The authors concluded that the novel multiplexed assay is robustly capable of detecting 15 different clinically relevant RET and ROS1 fusion variants. 

Rossi et al (2017) stated that immunohistochemistry (IHC) is a widely-tested, low-cost and rapid ancillary technique available in all laboratories of pathology.  This method is generally used for diagnostic purposes, but several studies have investigated the sensitivity and specificity of different immunohistochemical antibodies as a surrogate test in the determination of predictive biomarkers in NSCLC, particularly for epidermal EGFR gene mutations, ALK gene and ROS1 re-arrangements.  In this review, a critical examination of the works comparing the consistency of IHC expression and conventional molecular techniques to identify genetic alterations with predictive value in NSCLC was discussed.  Summarizing, data on sensitivity and specificity of antibodies against ALK and ROS1 are very consistent and time has comes to trust in IHC at least as a cost-effective screening tool to identify patients with re-arranged tumors in clinical practice.  On the other hand, mutant-specific antibodies against EGFR demonstrated a good specificity but a low-to-fair sensitivity, then raising some cautions on their employment as robust predictive biomarkers.  A brief comment on preliminary experiences with antibodies against BRAF, RET, HER2 and c-MET was also included.

Furthermore, National Comprehensive Cancer Network’s clinical practice guideline on “Non-small cell lung cancer” (Version 4.2016) states that “Emerging biomarkers include HER@ …. ROS1 and RET gene rearrangement”.


Pheochromocytoma is a rare, usually noncancerous (benign) tumor that develops in cells in the center of an adrenal gland, leading to attacks of raised blood pressure, palpitations and headache. Paraganglioma is a tumor of the tissue composing the paraganglion, a small round body containing chromaffin cells, found near the aorta and in the kidney, liver heart and gonads. 

Brito and associates (2015) noted that the presence of germline mutations in sporadic pheochromocytomas and paragangliomas (SPPs) may change the clinical management of both index patients and their family members.  However, the frequency of germline mutations in SPPs is unknown.  In a systematic review, these researchers described the frequency of germline mutations in SPPs and determined the value of testing index patients and their family members for these mutations.  They searched databases through June 2012 for observational studies of patients with SPPs who underwent germline genetic testing.  The criteria used to define sporadic tumors were

  1. the absence of a family history of PCC/PG
  2. the absence of syndromic features
  3. the absence of bilateral disease, and
  4. the absence of metastatic disease.

These investigators included 31 studies including 5,031 patients (mean age of 44 years).  These patients received tests for any of these 10 mutations: SDHAF2, RET, SDHD, SDHB, SDHC, VHL, TMEM127, MAX, isocitrate dehydrogenase (IDH) mutation and NF1.  The overall frequency of germline mutation in SPP was 551 of 5,031 (11 %); when studies with patients fulfilling 4 criteria for sporadic tumors were used, the frequency was 171 of 1,332 (13 %).  The most common germline mutation was SDHB 167 of 3,611 (4.6 %).  Little outcome data were available to assess the benefits of genetic testing in index cases and family members.  The authors concluded that the frequency of germline mutations in SPPs is approximately 11 to 13 % and the most common mutations affect less than 1 in 20 patients (5 %).  They stated that the value of testing for germline mutations in patients with SPPs and their family members is unknown, as the balance of potential benefits and harms remains unclear.

Table: CPT Codes / HCPCS Codes / ICD-10 Codes
Code Code Description

Information in the [brackets] below has been added for clarification purposes.   Codes requiring a 7th character are represented by "+":

CPT codes covered if selection criteria are met:

81404 - 81406 Molecular pathology procedures
88271 Molecular cytogenetics; DNA probe, each (e.g., FISH)

HCPCS codes not covered for indications listed in the CPB:

S3840 DNA analysis for germline mutations of the RET proto-oncogene for susceptibility to multiple endocrine neoplasia type 2

ICD-10 codes covered if selection criteria are met:

C73 - C75.9 Malignant neoplasm of the thyroid and other endocrine glands
E07.0 Hypersecretion of calcitonin
Q43.1 Hirschsprung's disease
Z80.8 Family history of malignant neoplasm of other organs or systems [thyroid cancer]

ICD-10 codes not covered for indications listed in the CPB:

C34.00 - C34.92 Malignant neoplasm of bronchus and lung [non-small cell lung cancer]
C75.5 Malignant neoplasm of aortic body and other paraganglia
D35.6 Benign neoplasm of aortic body and other paraganglia
D44.7 Neoplasm of uncertain behavior of aortic body and other paraganglia

The above policy is based on the following references:

  1. Delbridge L, Robinson B. Genetic and biochemical screening for endocrine disease: III. Costs and logistics. World J Surg. 1998;22(12):1212-1217.
  2. Eng C, Clayton D, Schuffenecker I, et al. The relationship between specific RET proto-oncogene mutations and disease phenotype in multiple endocrine neoplasia type 2. International RET mutation consortium analysis. JAMA. 1996;276(19):1575-1579.
  3. Goretzki PE, Hoppner W, Dotzenrath C, et al. Genetic and biochemical screening for endocrine disease. World J Surg. 1998;22(12):1202-1207.
  4. Guiffrida D, Gharib H. Current diagnosis and management of medullary thyroid carcinoma. Ann Oncol. 1998;9(7):695-701.
  5. Heshmanti HM, Gharib H, van Heerden JA, et al. Advances and controversies in the diagnosis and management of medullary thyroid carcinoma. Am J Med. 1997;103(1):60-69.
  6. Hofstra RM, Landsvater RM, Ceccherini I, et al. A mutation in the RET proto-oncogene associated with multiple endocrine neoplasia type 2B and sporadic medullary thyroid carcinoma. Nature. 1994;367(6461):375-376.
  7. Larimore TC, Wells SA. Cancer of the endocrine system. In: Cancer: Principles and Practice of Oncology. 5th ed. VT DeVita, S Hellman, SA Rosenberg, eds. Philadelphia, PA: Lippincott-Raven Publishers; 1997.
  8. Mulligan LM, Marsh DJ, Robinson BG, et al. Genotype-phenotype correlation in multiple endocrine neoplasia type 2: Report of the International RET Mutation Consortium. J Intern Med. 1995;238(4):343-346.
  9. Frohnauer MK, Decker RA. Update on the MEN 2A c804 RET mutation: Is prophylactic thyroidectomy indicated? Surgery. 2000;128(6):1052-1057; discussion 1057-1058.
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  12. Rodriguez GJ, Balsalobre MD, Pomares F, et al. Prophylactic thyroidectomy in MEN 2A syndrome: Experience in a single center. J Am Coll Surg. 2002;195(2):159-166.
  13. Frilling A, Weber F, Tecklenborg C, Broelsch CE. Prophylactic thyroidectomy in multiple endocrine neoplasia: The impact of molecular mechanisms of RET proto-oncogene. Langenbecks Arch Surg. 2003;388(1):17-26.
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  18. Kouvaraki MA, Shapiro SE, Perrier ND, et al. RET proto-oncogene: A review and update of genotype-phenotype correlations in hereditary medullary thyroid cancer and associated endocrine tumors. Thyroid. 2005;15(6):531-544.
  19. Ogilvie JB, Kebebew E. Indication and timing of thyroid surgery for patients with hereditary medullary thyroid cancer syndromes. J Natl Compr Canc Netw. 2006;4(2):139-147.
  20. DeLellis RA. Pathology and genetics of thyroid carcinoma. J Surg Oncol. 2006;94(8):662-669.
  21. Isabel M. Martinez Ferez, Roman Villegas Portero. Analysis of RET mutations to perform prophylactic thyroidectomy in individuals at risk for medullary thyroid cancer [summary]. AETSA 2006/09. Sevilla, Spain; Andalusian Agency for Health Technology Assessment (AETSA); 2007.
  22. Vestergaard P, Vestergaard EM, Brockstedt H, Christiansen P. Codon Y791F mutations in a large kindred: Is prophylactic thyroidectomy always indicated? World J Surg. 2007;31(5):996-1001; discussion 1002-1004.
  23. Moore SW, Appfelstaedt J, Zaahl MG. Familial medullary carcinoma prevention, risk evaluation, and RET in children of families with MEN2. J Pediatr Surg. 2007;42(2):326-332.
  24. Moore SW, Zaahl MG. Multiple endocrine neoplasia syndromes, children, Hirschsprung's disease and RET. Pediatr Surg Int. 2008;24(5):521-530.
  25. Fialkowski EA, DeBenedetti MK, Moley JF, Bachrach B. RET proto-oncogene testing in infants presenting with Hirschsprung disease identifies 2 new multiple endocrine neoplasia 2A kindreds. J Pediatr Surg. 2008;43(1):188-190.
  26. American Thyroid Association Guidelines Task Force; Kloos RT, Eng C, Evans DB, et al. Medullary thyroid cancer: Management guidelines of the American Thyroid Association. Thyroid. 2009;19(6):565-612.
  27. Frank-Raue K, Rondot S, Raue F. Molecular genetics and phenomics of RET mutations: Impact on prognosis of MTC. Mol Cell Endocrinol. 2010;322(1-2):2-7.
  28. Konstantinou E, Theodoros MS, Theofanis F, et al. Preventive thyroidectomy in patients with hereditary medullary thyroid carcinoma found heterozygote for mutant RET proto-oncogene. Pediatr Endocrinol Rev. 2010;8(2):108-113.
  29. Pandey R, Thurow T, de W Marsh R. Hirschsprung disease of the colon, a vaginal mass and medullary thyroid cancer -- a RET oncogene driven problem. J Gastrointest Oncol. 2011;2(4):254-257.
  30. Vaclavikova E, Kavalcova L, Skaba R, et al. Hirschsprung's disease and medullary thyroid carcinoma: 15-year experience with molecular genetic screening of the RET proto-oncogene. Pediatr Surg Int. 2012;28(2):123-1288.
  31. Lips CJ. Clinical manifestations and diagnosis of multiple endocrine neoplasia type 2. UpToDate [online serial]. Waltham, MA: UpToDate; reviewed February 2013.
  32. Tuttle RM. Medullary thyroid cancer: Clinical manifestations, diagnosis, and staging. UpToDate [online serial]. Waltham, MA: UpToDate; reviewed January 2014. 
  33. Krampitz GW, Norton JA. RET gene mutations (genotype and phenotype) of multiple endocrine neoplasia type 2 and familial medullary thyroid carcinoma. Cancer. 2014;120(13):1920-1931.
  34. Coyle D, Friedmacher F, Puri P. The association between Hirschsprung's disease and multiple endocrine neoplasia type 2a: A systematic review. Pediatr Surg Int. 2014;30(8):751-756.
  35. Igarashi T, Okamura R, Jikuzono T, et al. An extended family with familial medullary thyroid carcinoma and Hirschsprung's disease. J Nippon Med Sch. 2014;81(2):64-69.
  36. Yoshida A, Kohno T, Tsuta K, et al. ROS1-rearranged lung cancer: A clinicopathologic and molecular study of 15 surgical cases. Am J Surg Pathol. 2013;37(4):554-562.
  37. Lira ME, Choi YL, Lim SM, et al. A single-tube multiplexed assay for detecting ALK, ROS1, and RET fusions in lung cancer. J Mol Diagn. 2014;16(2):229-243.
  38. Brito JP, Asi N, Bancos I, et al. Testing for germline mutations in sporadic pheochromocytoma/paraganglioma: A systematic review. Clin Endocrinol (Oxf). 2015;82(3):338-345.
  39. Wijesinghe P, Bepler G, Bollig-Fischer A. A mass spectrometry assay to simultaneously analyze ROS1 and RET fusion gene expression in non-small-cell lung cancer. J Thorac Oncol. 2015;10(2):381-386.
  40. Rossi G, Ragazzi M, Tamagnini I, et al.  Does immunohistochemistry represent a robust alternative technique in determining drugable predictive gene alterations in non-small cell lung cancer? Curr Drug Targets. 2017;18(1):13-26.
  41. National Comprehensive Cancer Network. Clinical practice guideline: Non-small cell lung cancer. Version 4.2016. NCCN: Fort Washington, PA.
  42. Scollo C, Russo M, De Gregorio L, et al. A novel RET gene mutation in a patient with apparently sporadic pheochromocytoma. Endocr J. 2016;63(1):87-91.
  43. Sromek M, Czetwertyńska M, Tarasińska M, et al. Analysis of newly identified and rare synonymous genetic variants in the RET gene in patients with medullary thyroid carcinoma in Polish population. Endocr Pathol. 2017;28(3):198-206.