Short answer
RET codon 918, usually written M918T, is strongly associated with MEN2B when it is a confirmed germline pathogenic variant. MEN2B is the highest-risk RET syndrome in most counseling frameworks, so the question is not just what codon appears on the report. It is whether the result came from germline testing, whether the report is pathogenic or uncertain, whether the person already has MEN2B features, and how quickly endocrine genetics should get involved.
How to frame the result
| Finding | Common next question | Why it matters |
|---|---|---|
| Germline RET M918T | Is MEN2B follow-up already arranged? | Timing can be urgent, especially in children and teens. |
| Tumor-only codon 918 | Was inherited testing considered separately? | Tumor-only results do not automatically define family risk. |
| Child with MEN2B features | Has pediatric endocrine genetics been involved? | Clinical features can prompt earlier recognition than the report alone. |
What MEN2B usually means
MEN2B can include medullary thyroid cancer risk, pheochromocytoma risk, mucosal neuromas, distinctive physical findings, and gastrointestinal symptoms. The NCI and GeneReviews resources both treat codon 918 as the classic MEN2B pattern that deserves expert coordination rather than casual watchful waiting. If the result is a variant of uncertain significance instead of a confirmed pathogenic change, that is a different situation and should not be managed like a settled MEN2B diagnosis.
Because some MEN2B cases are de novo, family history can look deceptively quiet. That is one reason a positive codon 918 result still needs a real genetics review, even if no one else in the family has an obvious thyroid cancer history.
What to do next
- Confirm the exact notation on the report: M918T, p.Met918Thr, codon 918, pathogenic, likely pathogenic, or uncertain.
- Check whether the sample was blood or saliva germline testing, tumor tissue, or paired tumor-normal testing.
- Ask who is coordinating calcitonin, thyroid imaging, adrenal screening, and any pediatric surgery timing.
- Clarify whether parents, siblings, children, or other relatives need targeted testing or de novo evaluation.
How to read results
| Result type | What it usually means | Next question |
|---|---|---|
| Pathogenic or likely pathogenic germline M918T | Supports MEN2B-level inherited risk and prompts specialist follow-up. | How quickly should endocrine genetics and thyroid planning happen? |
| Codon 918 on tumor-only testing | May reflect a somatic cancer change rather than inherited risk. | Is germline confirmation recommended? |
| VUS or uncertain 918 change | The finding is not yet a confirmed family-risk result. | Will the lab or specialist reinterpret it later? |
| Negative RET in a person with MEN2B-like features | Does not fully explain the clinical picture. | Should broader genetics or a different specimen be considered? |
Questions to ask
- Is the result from blood/saliva germline testing or from tumor sequencing?
- Does the report say M918T, p.Met918Thr, codon 918, pathogenic, likely pathogenic, or VUS?
- Who is coordinating calcitonin, thyroid ultrasound, adrenal screening, and any surgery discussion?
- Do parents, siblings, or children need targeted testing or de novo assessment?
FAQ
What does RET codon 918 usually mean?
Codon 918, usually written M918T, is strongly associated with MEN2B when it is a confirmed germline pathogenic variant.
Does codon 918 automatically prove inherited disease?
No. A tumor-only RET finding can reflect cancer biology instead of germline risk, so the sample type has to be confirmed.
Why is this result treated as urgent?
MEN2B can be associated with early medullary thyroid cancer risk, so pediatric endocrine and genetics review may be time-sensitive.
Can codon 918 be de novo?
Yes. Some MEN2B results are de novo, which is why parent testing and family review still matter.
What follow-up tests usually come next?
Calcitonin, thyroid evaluation, adrenal screening, and specialist genetics review are common next steps, depending on the person and age.
Who should interpret the report?
A genetics professional with endocrine expertise is usually the right person to connect the variant, sample type, age, and family history.