Medullary Thyroid Carcinoma

Total (or near-total) thyroidectomy with resection of the central cervical lymph node compartment (in multiple anatomical levels (II-VI)) is the procedure of choice for initial therapy in patients with MTC [39,99]. T/NTT is indicated because MTC is often multifocal. Life-long replacement L-T4 therapy is necessary postop-eratively. In addition to regional lymph nodes, other common sites of metastases include the lung,liver,bones, and CNS. Therefore,these sites of potential spread need to be screened using imaging methods at the time of initial presentation, as indicated by the clinical features and degree of elevation in plasma calcitonin levels in each case. All patients with MEN2 syndromes should be screened for pheochromocytoma. If pheochromocytoma is present,bilateral adrena-lectomy may be necessary because of the multi-centricity and bilaterality of these tumors in the context of MEN2 syndromes. Once a patient has been diagnosed as having MEN2A/MEN2B or FMTC through RET proto-oncogene mutation testing, such testing should be performed on all living relatives, to detect gene carriers who are predisposed to CCH and MTC [39]. Molecular genetic testing permits early identification of gene carriers before MTC becomes clinically apparent, thus allowing for prophylactic total thyroidectomy and additional surgical procedures as necessary [39,99]. RET germline mutation testing has replaced plasma calcitonin testing as the study of choice for the detection of gene carriers in MEN2 pedigrees [53].

The ideal age at which prophylactic T/NTT should be performed in children with RET germline mutations remains controversial. In the recent past, some clinicians have recommended surgery in carriers of RET mutations associated with MEN2B within the first year of life and for carriers of RET mutations associated with MEN2A by 5 years of age [100].Heptulla et al. [54] proposed prophylactic T/NTT during the first decade of life in patients with FMTC.

A recent consensus conference suggested variable timing of the surgery depending on the actual codon of the RET gene where the mutation is located [39], as follows:

• Children with MEN2B and/or RET codon 883,918, or 922 mutations are classified as having the highest risk for aggressive MTC development (level 3 risk) and should have T/NTT within the first 6 months - preferably within the first month - of life.

• Children with RET codon 611,618,620, or 634 mutations are classified as having a moderately high risk for aggressive MTC development (level 2 risk) and should have T/NTT performed before the age of 5 years.

• Children with RET codon 609, 768, 790, 791,804, or 891 mutations are classified as having the lowest risk of aggressive MTC (level 1 risk). There is little consensus on the management of patients with these

WDTC Diagnosis—►

Total/Near-Total Thyroidectomy —►

RAI ablation therapy

1

INITIAL Rx

Post-Rx RAI WBS

Long-term THST

9 mos

(or chest CT w/o IV contrast)

(or chest CT w/o IV contrast)

Long-term THST

Anatomically ^ definable disease?

Hypothyroid preparation

Diagnostic RAI WBS Positive?

Repeat neck +/- mediastinal dissection

Treat with RAI

Subsequent

Follow-up visits

Restaging

Subsequent

Follow-up visits

Restaging

Neck U/S and CXR (or chest CT w/o IV contrast)

Establish NED status and confirm at each successive evaluation

Serum Tg under Hypothyroid conditions > 8 ng/ml

Long-term THST ^_

FDG-PET scan (optional) *

Treat with RAI (debatable) -

Post-Rx RAI WBS

Post-Rx RAI WBS

Neck U/S and CXR (or chest CT w/o IV contrast)

Anatomically definable disease?

Yes h Repeat neck +/- mediastinal dissection

Establish NED status and confirm at each successive evaluation

No I rhTSH administration

Diagnostic RAI WBS Positive?

Serum Tg under rhTSH stimulation conditions > 2 ng/ml No

Render Hypothyroid and treat with RAI *

Render Hypothyroid _ and treat with RAI* (debatable)

Post-Rx RAI WBS

Post-Rx RAI WBS

Post-Rx RAI WBS

Post-Rx RAI WBS

Figure 23.1 Algorithm for the follow-up of pediatric patients with well-differentiated thyroid carcinoma (WDTC) after total/near-total thyroidectomy and initial 131I remnant ablation. In the proposed scheme, special emphasis is placed on the detection and eradication - whenever feasible - of persistent/recurrent metastatic disease in all patients who do not achieve no evidence of disease (NED) status. Different cutoff serum Tg values are used as corroborating evidence of residual/recurrent disease, depending on how TSH stimulation is achieved (thyroid hormone withdrawal versus recombinant human thyrotropin (rhTSH) administration). For more details, refer to the text. Abbreviations: CT: computed tomography, CXR: chest X-ray, FDG-PET: 18F-fluorodeoxyglucose positron emission tomography, IV: intravenous, RAI: radioiodine (131I), Rx: therapy,TH: thyroid hormone,THST: thyroid hormone suppressive therapy, U/S: ultrasonography,WBS: whole-body scan, w/o: without; mos, months.

* RAI treatment can also be administered under stimulation with rhTSH.This is an "off-label" use of rhTSH, and should be preferably limited to tertiary center specialists with experience in the treatment of pediatric TC.

**The benefits of using FDG-PET for diagnostic purposes in pediatric TC patients should be balanced against the radiation exposure from the administration of FDG (a positron emitter). Hence, the use of FDG-PET scans in pediatric TC patients should be preferably limited to tertiary center specialists.

9 mos

9-12 mos

No mutations. Some advocate T/NTT by the age of 5 years. Others suggest that thyroidectomy by age 10 is appropriate. Still others recommended periodic pentagas-trin-stimulated calcitonin testing with surgery at the first occurrence of an abnormal test result.

The above guidelines were corroborated by the recent finding that the risk of age-related pro gression from CCH to MTC is dependent upon the transforming potential of the individual RET mutation [101,102]. Postoperative EBRT may be offered to patients with high risk of recurrence in the thyroid bed and to those with cervical, supraclavicular, or mediastinal lymphadenopa-thy [103]. Of note, RAI ablative therapy has no role in the postoperative management of MTC.

Peripheral levels of calcitonin and carci-noembryonic antigen (CEA) are used for mon itoring disease activity after the initial operation. Patients with persistently elevated or rising calcitonin levels have residual or recurrent metastatic disease, and, in these cases, additional imaging should be performed for localization of the disease, which could lead to further surgical treatment. Imaging is usually done with conventional modalities, such as neck U/S and CT/MRI, although 111In-pentetrotide can also be of considerable help [104].

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