MEN2: Multiple Endocrine Neoplasia Type 2 & RET Mutations

Multiple endocrine neoplasia type 2, usually called MEN2, is a hereditary cancer syndrome caused by mutations in a single gene called RET. The syndrome runs in families in a dominant pattern, meaning a child who inherits just one copy of the mutated gene from either parent is affected. MEN2 predisposes people to specific tumors of the endocrine system, most consistently medullary thyroid cancer, and often adrenal gland tumors called pheochromocytomas and overactive parathyroid glands. The condition is rare, but its genetics are well understood, and that understanding has transformed how families are screened and treated.

What the RET Gene Does and Why It Matters

RET encodes a protein on the surface of certain cells that normally helps relay growth signals. In MEN2, specific point mutations cause RET to become permanently switched on, sending nonstop growth signals to cells in the thyroid, adrenal glands, and parathyroids. These are gain-of-function mutations: they do not break the gene but instead make it overactive.¹ Laboratory experiments in the 1990s showed that cells engineered to carry these MEN2 mutations took on a transformed appearance, formed colonies, and grew tumors when implanted in mice, confirming RET’s direct role in driving cancer.²

Which specific spot on RET is mutated turns out to matter enormously. Different mutations correlate tightly with how aggressive the thyroid cancer is, how early it appears, and which other tumors develop. This tight genotype-phenotype relationship is central to how doctors manage the syndrome: the mutation itself acts as a roadmap for what to expect and when to intervene.³

The Clinical Subtypes

MEN2 is split into three recognized forms based on which combination of problems typically appears. MEN2A is the most common, accounting for the large majority of cases. People with MEN2A develop medullary thyroid cancer, and roughly half also develop pheochromocytomas. A smaller proportion develop overactive parathyroid glands. MEN2B is rarer and more aggressive: it includes medullary thyroid cancer and pheochromocytomas but swaps out parathyroid disease for distinctive physical features like mucosal neuromas and a tall, thin body type. Familial medullary thyroid carcinoma, sometimes considered a mild variant of MEN2A, involves medullary thyroid cancer alone with very few other endocrine problems.⁴

A large international analysis of RET mutations found that pheochromocytoma and parathyroid overactivity are most common in patients with mutations at codon 634, the classic MEN2A mutation. Mutations at codons 768 and 804, by contrast, have been seen only in familial medullary thyroid carcinoma. The codon 918 mutation is essentially exclusive to MEN2B.⁵ In a separate study, 20 out of 21 pheochromocytoma patients carried either codon 634 or 918 mutations, and 7 out of 10 patients with parathyroid disease had codon 634 mutations.⁶

Medullary Thyroid Cancer

Medullary thyroid cancer is the hallmark of MEN2 and the leading cause of death in affected families if left untreated. It arises from the parafollicular C cells of the thyroid, which produce a hormone called calcitonin. Because calcitonin is measurable in the blood, it serves as a useful tumor marker both for initial diagnosis and for monitoring after surgery. The cancer in MEN2 tends to be bilateral, developing in both lobes of the thyroid, which is why treatment requires removing the entire gland rather than just one side.⁷

One of the most striking recent findings challenges the long-held assumption that virtually everyone carrying a pathogenic RET variant will develop medullary thyroid cancer. A 2025 study compared cancer risk in RET variant carriers identified incidentally through large genomic databases with carriers identified through clinical testing of affected families. In the UK Biobank, the estimated risk of medullary thyroid cancer by age 75 in incidentally identified carriers was about 2%, and in a US health-system cohort it was about 19%. Both figures were dramatically lower than the roughly 96% risk seen in carriers identified through family screening with the same mutations. Overall mortality among the UK Biobank carriers who had not undergone thyroidectomy was essentially the same as that of the general population.⁸ These findings suggest that clinical family-based estimates overstate the risk for many carriers, likely because the families that come to medical attention tend to have the most aggressive disease. However, virtually all of the incidentally identified carriers had moderate-risk mutations, so the findings do not apply to higher-risk categories.

Pheochromocytoma

About half of people with MEN2A or MEN2B develop a pheochromocytoma, a tumor of the adrenal gland that produces surges of adrenaline and related hormones. These tumors are almost always benign and confined to the adrenal glands, but roughly a third are bilateral at initial diagnosis.⁹ Even benign pheochromocytomas can be dangerous: the catecholamine surges they produce cause episodes of high blood pressure, rapid heartbeat, sweating, and headaches. People with MEN2-related pheochromocytomas tend to have more cardiovascular complications compared with some other hereditary forms of the tumor.¹⁰

Because pheochromocytomas in MEN2 often release their hormones in bursts rather than continuously, standard blood pressure readings can miss the problem. The preferred screening test measures substances called metanephrines, which are produced steadily even when catecholamine secretion is episodic. Plasma free metanephrines are the first-choice test, with urinary fractionated metanephrines as an alternative.¹¹ Any patient being considered for thyroid surgery must first be screened for pheochromocytoma, because undiagnosed tumors can cause life-threatening blood pressure crises during anesthesia.

Parathyroid Disease

Overactive parathyroid glands occur in a subset of MEN2A patients, particularly those with codon 634 mutations. Reported rates vary widely, from about 8% to 31% depending on the population studied, with lower rates seen in family members identified through screening rather than after symptoms develop.¹² The excess parathyroid hormone drives calcium levels up, and the most common complication is kidney stones, reported in up to 80% of symptomatic patients. Osteoporosis is another recognized consequence. That said, many patients with mildly elevated parathyroid hormone have no symptoms at all. In one cohort, three-quarters of patients with parathyroid overactivity were asymptomatic.¹³

Parathyroid disease rarely shows up as the first sign of MEN2. A multicenter study found that overactive parathyroids were the initial manifestation in under 1% of MEN2A patients. When it did appear first, the majority of those patients turned out to already have medullary thyroid cancer with lymph node involvement at the time their parathyroid problem was surgically addressed.¹⁴ This underscores why isolated parathyroid disease in a young patient should prompt consideration of genetic testing.

Recognizing MEN2B

MEN2B accounts for a small fraction of all MEN2 cases but has the most aggressive thyroid cancer and often the most delayed diagnosis. The physical features are distinctive: affected individuals tend to have a tall, slender body habitus, bumpy nodules on the tongue, lips, and inner cheeks (mucosal neuromas), and sometimes thickened, prominent lips. Other features include a high-arched palate, vocal cord nodules, and dry eyes from inadequate tear production.¹⁵¹⁶

Gastrointestinal problems, including chronic constipation and feeding difficulties in infancy, are common in MEN2B and often appear before any cancer develops. In many sporadic cases (where the mutation is new and there is no family history), these childhood symptoms go unexplained for years. A recent case series of six children with sporadic MEN2B found that all had classic physical features and gastrointestinal symptoms, yet diagnosis was significantly delayed.¹⁷ Because MEN2B thyroid cancer can develop in infancy, recognizing these features early is critical.

Genetic Screening and Family Testing

Guidelines recommend that every patient diagnosed with medullary thyroid cancer, whether or not there is a known family history, should undergo RET gene testing. Once a mutation is confirmed in one person, first-degree relatives should be tested promptly. About half of those relatives will carry the mutation and face the associated cancer risks.¹⁸

The landscape of recognized RET mutations is still expanding. A recent analysis of panel genetic testing found 246 individuals carrying pathogenic RET variants not listed in the current American Thyroid Association guidelines, including several uncommon mutations. This highlights a gap between established guidelines and the diversity of mutations being discovered as genetic testing becomes more widespread.¹⁹ For families, the practical implication is that a negative test for the most commonly screened mutations does not always rule out a hereditary form of the disease. Broader sequencing of the entire RET gene may be warranted.

Preventive Thyroidectomy in Children

Because medullary thyroid cancer in MEN2 is essentially inevitable in high-risk mutation carriers if the thyroid is left in place, the standard of care is to remove the thyroid gland before cancer develops or while it is still microscopic and curable. The timing depends on the mutation’s risk level.

Current guidelines group RET mutations into three tiers. Children with the highest-risk mutation (codon 918, the MEN2B mutation) should have their thyroid removed as soon as possible in the first year of life. Children in the high-risk group (codon 634) should have surgery by age five, or earlier if calcitonin levels rise on monitoring. For the moderate-risk group, surgery can be guided by calcitonin monitoring starting around age five, with the operation performed when levels begin climbing.²⁰

The reasoning behind early surgery is the concept of a “window of opportunity.” If the entire thyroid is removed before cancer has spread to nearby lymph nodes, a total thyroidectomy alone is usually curative. Once lymph node metastases develop, more extensive neck dissection becomes necessary, and the chance of a complete cure drops sharply. When more than ten lymph nodes are involved, cure rates fall to near zero.²¹ A landmark study of 50 children who underwent preventive thyroidectomy found that 88% had undetectable calcitonin levels afterward, and children who had surgery before age eight fared better than those who waited longer.²²

Early thyroidectomy in young children is not without consequences. A retrospective analysis of very young patients found that about 27% developed temporary low calcium after surgery and 20% had permanent low calcium requiring ongoing supplementation. None, however, had evidence of recurrent cancer after an average follow-up of over ten years.²³ All patients who undergo thyroidectomy require lifelong thyroid hormone replacement. For families weighing these trade-offs, the central consideration is that medullary thyroid cancer, once it has spread, is difficult to cure, whereas hypothyroidism and calcium supplementation are manageable with medication.

Surgery for Pheochromocytoma

When a pheochromocytoma is found, surgical removal is the treatment. In MEN2, the question of how much adrenal tissue to take is clinically important because the tumors often eventually develop on both sides. Removing both adrenal glands entirely leaves a patient dependent on lifelong steroid replacement and at risk of adrenal crisis, a potentially fatal emergency.

Adrenal-sparing surgery, where the tumor is removed but a rim of healthy adrenal cortex is preserved, has become the preferred approach. Studies report that this technique results in less than 5% significant tumor recurrence after ten years of follow-up, while preserving normal cortisol production in more than half of patients.²⁴ The risk of a slowly growing, benign recurrence is generally considered acceptable compared to the dangers of lifelong adrenal insufficiency.²⁵ Patients do need close follow-up imaging and biochemical monitoring afterward.

Targeted Therapies for Advanced Medullary Thyroid Cancer

For patients whose medullary thyroid cancer has spread beyond what surgery can address, treatment options have expanded considerably. Older drugs called multikinase inhibitors (cabozantinib and vandetanib) were the first systemic treatments approved for advanced medullary thyroid cancer, but they affect many cellular targets and carry a significant burden of side effects. More recently, drugs designed to specifically block the RET protein have arrived.

Selpercatinib and pralsetinib are RET-selective inhibitors that received FDA approval based on strong clinical trial results.²⁶ A phase 3 trial comparing selpercatinib head-to-head with cabozantinib or vandetanib in patients with RET-mutant medullary thyroid cancer found that selpercatinib was clearly superior. At one year, about 87% of patients on selpercatinib were free of disease progression compared with about 66% on the older drugs. The overall tumor response rate was roughly 69% with selpercatinib versus 39% with the comparators.²⁷

Despite these advances, resistance eventually develops in some patients. Researchers have identified mutations at a specific part of the RET protein, called the solvent front (particularly at position G810), that prevent selpercatinib from binding effectively. These resistance mutations have been found in both medullary thyroid cancer and RET-driven lung cancer. Worryingly, all five resistance mutations identified in one lab study were also resistant to pralsetinib, meaning the two approved RET-selective drugs share the same vulnerability.²⁸²⁹ Next-generation RET inhibitors designed to overcome these resistance mutations are in clinical development.

Family Planning

Because MEN2 follows a dominant inheritance pattern, each child of a mutation carrier has a 50% chance of inheriting the syndrome. For families who want biological children without passing the mutation on, preimplantation genetic diagnosis is an option. This technique, performed during in vitro fertilization, tests embryos for the specific RET mutation before transfer. A published case demonstrated successful use of this approach: four embryos were identified as unaffected, one was transferred, and a healthy baby was born at full term.³⁰

Beyond the reproductive mechanics, the psychological weight of carrying and potentially passing on a cancer-predisposing mutation is substantial. Research into quality of life in MEN2 families identifies recurring themes: fear about the future, guilt about potentially transmitting the mutation to children, side effects of cancer treatments, and difficulty coping with what is often a lifelong, incurable cancer. Access to specialized care can also be a challenge, since MEN2 is rare and expertise is concentrated at a relatively small number of medical centers.³¹

Cutaneous Lichen Amyloidosis

An unusual feature of certain MEN2A families is a skin condition called cutaneous lichen amyloidosis: an intensely itchy, scaly rash that characteristically appears on the upper back between the shoulder blades. It is rare overall but tightly linked to specific codon 634 mutations. A systematic review found that the large majority of affected families carried one of several 634 variants, with C634R being the most common.³² The rash can appear in childhood, sometimes years before any cancer develops, and recognizing it as a potential marker of MEN2A can prompt earlier genetic testing. Most dermatologists will not encounter this association often, so the connection is easily missed when patients present with what looks like ordinary itchy skin.