RAS Mutations in Thyroid Cancer

by Jason Wasserman MD PhD FRCPC
April 3, 2026

If your pathology report or molecular test results mention a RAS mutation — most commonly NRAS, HRAS, or KRAS — this refers to a change in one of three closely related genes that help control how thyroid cells grow and divide. RAS mutations are among the most common molecular findings in thyroid cancer and in thyroid nodules that turn out not to be cancer. Unlike some other thyroid biomarkers, a RAS mutation does not currently identify you as a candidate for a specific targeted drug. Instead, it provides information that helps confirm a diagnosis, estimate how a tumour is likely to behave, and, in combination with other molecular findings, identify the small subset of patients whose cancer carries the highest risk of aggressive behavior. This article explains what a RAS result means in the context of your specific thyroid diagnosis.

What the test looks for

The RAS family consists of three genes — NRAS, HRAS, and KRAS — each of which encodes a closely related protein. RAS proteins act as molecular switches inside cells, relaying growth signals from the cell surface into the cell’s interior. In their normal state, RAS proteins switch on briefly when a growth signal arrives and then switch off again. When a RAS gene is mutated, the resulting protein remains in the “on” state, continuously driving cell growth and division,,even in the absence oft a signat.

In thyroid cancer, NRAS mutations are the most common, followed by HRAS mutations. KRAS mutations are relatively rare in thyroid tumors. The most frequently affected positions in thyroid cancer are codon 61 of NRAS and HRAS, and codon 12/13 of KRAS, though the specific mutation does not currently change clinical management.

RAS mutations activate the same MAPK growth-signaling pathway as BRAF V600E mutations. However, they do so in a less potent and less specific way, and the tumors they produce tend to have different characteristics — including a more follicular growth pattern, a lower likelihood of lymph node spread, and a greater tendency to spread through the bloodstream to distant sites such as the lungs and bones.

An important feature of RAS mutations in thyroid disease is that they are not specific for cancer. They are found not only in malignant tumors but also in benign follicular adenomas, in non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) — a borderline lesion that is not considered cancer — and occasionally in other benign nodules. This means that identifying a RAS mutation in a thyroid nodule biopsy does not, by itself, confirm malignancy. However, it meaningfully increases the probability that the nodule is neoplastic and may require surgical removal.

Whis the testis done

RAS testing in thyroid cancer and thyroid nodules serves three related purposes: supporting surgical decision-making in indeterminate thyroid nodule biopsies, contributing to the molecular classification of diagnosed thyroid cancers, and, in combination with TERT promoter mutation testing, identifying tumors with a significantly elevated risk of aggressive behavior.

Indeterminate thyroid nodule biopsies

When a fine-needle aspiration biopsy of a thyroid nodule yields an indeterminate result — meaning the cells look suspicious but cannot be definitively classified as benign or malignant — molecular testing panels that include RAS mutation analysis are used to estimate the probability of cancer and guide the decision about whether surgery is needed.

In this setting, a positive RAS mutation result is meaningful but must be interpreted carefully. Because RAS mutations can be present in both benign and malignant follicular-patterned tumors, a positive result does not confirm cancer — it raises the probability of a neoplastic lesion (one that will need to be surgically removed and examined in full) and influences the type of surgery recommended. Molecular testing panels used in this context — such as ThyroSeq and Afirma — combine RAS mutation results with other molecular markers to generate an overall risk estimate that is more informative than any single alteration alone.

Molecular classification of diagnosed thyroid cancers

In patients who already have a confirmed thyroid cancer diagnosis after surgery, RAS mutation results contribute to understanding the molecular subtype of the cancer. RAS mutations are characteristically found in follicular-patterned tumors— including follicular thyroid carcinoma, the follicular variant of papillary thyroid carcinoma, and poorly differentiated thyroid carcinoma — rather than in classic papillary thyroid carcinoma, where BRAF V600E is the dominant alteration. The molecular profile of a thyroid cancer, including its RAS status, helps confirm the tumour type and informs the expected clinical behaviour.

Prognostic risk stratification in combination with TERT

The most clinically significant use of RAS mutation testing in confirmed thyroid cancer is in combination with TERT promoter mutation testing. TERT promoter mutations are alterations in a gene that controls how cells maintain their chromosomes during repeated cell division. When a RAS mutation and a TERT promoter mutation are both present in the same tumour, the combination is strongly associated with aggressive behavior — including a significantly higher risk of recurrence, distant metastasis, and cancer-related death — compared to tumors with either mutation alone or with neither.

This co-mutation pattern is particularly important in well-differentiated and poorly differentiated thyroid carcinomas, where it can identify a high-risk subgroup within what might otherwise appear to be heterogeneous. Identifying this combination may influence the intensity of adjuvant treatment, the frequency of follow-up, and decisions about systemic therapy in advanced disease.

Who should be tested

RAS mutation testing is appropriate in the following clinical contexts:

Patients with indeterminate thyroid nodule biopsies. When a fine needle aspiration biopsy results are indeterminate — corresponding to Bethesda category III (atypia of undetermined significance) or category IV (follicular neoplasm/suspicious for follicular neoplasm) — molecular testing panels, including RAS analysis, can help estimate cancer risk and guide surgical planning. In many thyroid centers, molecular testing is now offered routinely for nodules in these categories.
Patients with confirmed follicular-patterned thyroid cancers. RAS testing is part of the comprehensive molecular profiling performed on follicular thyroid carcinoma, the follicular variant of papillary thyroid carcinoma, poorly differentiated thyroid carcinoma, and oncocytic (Hürthle cell) carcinoma. When combined with TERT promoter mutation testing, the result contributes meaningfully to prognostic risk stratification.
Patients with advanced or radioiodine-refractory thyroid cancer. In patients whose cancer has spread or has stopped responding to radioactive iodine, comprehensive molecular profiling — including RAS and TERT — helps characterize the tumor’s biology and identify actionable alterations that may support targeted therapy or eligibility for clinical trials.

RAS mutations are not typically tested in isolation. In most centers, they are identified as part of a broader next-generation sequencing panel that also evaluates BRAF, RET, NTRK, TERT, and other relevant genes simultaneously.

How the test is performed

RAS mutation testing in thyroid cancer is performed using tumour tissue — either from the surgical specimen after the thyroid or nodule has been removed, or from a biopsy sample obtained before surgery.

The primary method is next-generation sequencing (NGS), which reads the genetic code of the tumour across many genes simultaneously. NGS can detect RAS mutations alongside BRAF, RET fusions, NTRK fusions, TERT promoter mutations, and other clinically relevant alterations in a single test. This comprehensive approach is important because the clinical significance of a RAS mutation often depends on what other alterations are — or are not — present in the same tumour.

For thyroid nodule evaluation before surgery, commercially available molecular testing panels — including ThyroSeq and the Afirma Genomic Sequencing Classifier — are performed on material obtained from fine-needle aspiration biopsy. These panels are specifically designed for the indeterminate nodule setting and combine RAS mutation results with other markers to generate an overall risk estimate.

RAS mutations are somatic alterations — they arise in the tumour cells during a person’s lifetime and are not inherited. Blood-based germline testing is not indicated when a RAS mutation is identified in a thyroid tumour. A RAS mutation in a thyroid cancer does not have implications for family members.

How results are reported

RAS mutation results are typically reported in one of the following ways:

RAS mutation detected (or NRAS/HRAS/KRAS mutation detected). The report will specify which of the three RAS genes carries the mutation and the exact change identified — for example, “NRAS p.Q61R mutation detected” or “HRAS p.Q61K mutation detected.” The variant allele frequency may also be reported, reflecting the proportion of tumour cells carrying the mutation.
No RAS mutation detected. No mutations were found in the NRAS, HRAS, or KRAS genes within the regions analyzed. Results for the other genes tested will accompany a negative result within the broader panel.

When testing is performed as part of a molecular panel for an indeterminate thyroid nodule, the result may be presented alongside an overall risk classification or probability estimate generated by the panel, rather than as a standalone RAS result.

When NGS is used on a confirmed cancer, the RAS result will appear alongside results for other genes — including TERT promoter mutation status, which is the most important co-finding to look for alongside a RAS mutation.

What the result means

RAS mutation detected in an indeterminate thyroid nodule biopsy

A RAS mutation identified in an indeterminate thyroid nodule biopsy means the nodule contains a molecular change associated with follicular-patterned thyroid neoplasms — both benign and malignant. It does not confirm cancer on its own.

In practice, a RAS mutation in this context increases the estimated probability that the nodule is a true neoplasm — something that needs to be removed and fully examined — but the probability of malignancy varies considerably depending on the specific mutation and the overall panel result. In most cases, a RAS-positive indeterminate nodule will prompt surgical removal (typically lobectomy) to obtain the full histological picture. The final diagnosis — whether follicular adenoma, NIFTP, follicular carcinoma, or follicular variant papillary carcinoma — can only be made after the entire nodule capsule and surrounding tissue have been examined under the microscope.

Some patients find it unsettling to receive a molecular result that does not give a definitive answer. It is worth understanding that this uncertainty is inherent to the biology of follicular-patterned thyroid tumors—the cells simply look similar in benign and malignant forms, so any molecular marker cannot completely resolve the distinction until the whole tumour is available for examination. The value of the RAS result in this context is to refine the surgical decision, not to provide a cancer diagnosis.

RAS mutation detected in a confirmed thyroid cancer

In a patient who already has a confirmed diagnosis of thyroid cancer, a RAS mutation provides information about the molecular subtype of the cancer. It contributes to prognostic assessment — particularly when combined with TERT promoter mutation results.

On its own, a RAS mutation in a well-differentiated thyroid cancer (follicular carcinoma or follicular variant papillary carcinoma) is associated with a clinical behavior that differs somewhat from BRAF V600E-driven cancers. RAS-mutated well-differentiated thyroid cancers tend to spread less often to lymph nodes and more often through the bloodstream to distant sites — particularly the lungs and bones — which influences the type of surveillance imaging used during follow-up. They also tend to retain the ability to take up radioactive iodine more readily than BRAF-mutated tumors, which is clinically important because radioactive iodine is a main treatment for distant metastases.

A RAS mutation alone, in a well-differentiated cancer that has been fully resected, does not typically change the treatment approach compared to a RAS-negative cancer of the same type and stage.

RAS mutation with co-occurring TERT promoter mutation

When both a RAS mutation and a TERT promoter mutation are present in the same tumour, the clinical picture changes significantly. This combination is a strong marker of aggressive behavior in thyroid cancer — substantially more so than either mutation alone.

Studies of patients with differentiated and poorly differentiated thyroid carcinomas have consistently shown that the RAS-plus-TERT combination is associated with higher rates of distant metastasis, poorer response to treatment, and reduced overall survival compared to tumors with only one of these alterations. The TERT promoter mutation appears to amplify the growth-promoting effect of RAS, and the two together push the tumour biology toward more aggressive disease.

When both mutations are found, this information influences the intensity of follow-up and the threshold for initiating systemic therapy in advanced disease. It may affect eligibility for clinical trials investigating treatments specifically for this molecular subgroup. Your oncologist or endocrinologist will discuss what the combined result means for your specific situation and stage.

No RAS mutation detected

A negative RAS result in an indeterminate thyroid nodule reduces — but does not eliminate — the probability of a follicular-patterned neoplasm. The overall molecular panel result, rather than the RAS result alone, guides surgical planning in this context.

In a confirmed thyroid cancer, a negative RAS result indicates that RAS mutations are not the molecular driver. Other alterations — BRAF, RET fusions, NTRK fusions, or others — may be identified on the same panel, and their implications are discussed separately. The absence of a RAS mutation does not confer any particular prognostic benefit on its own.

RAS mutations and targeted therapy

Unlike BRAF V600E mutations, for which targeted inhibitors (dabrafenib plus trametinib) are approved in thyroid cancer, there are currently no RAS-targeted therapies approved specifically for thyroid cancer. RAS proteins have historically been difficult to target directly with drugs. However, this is an active area of research — particularly for KRAS, where inhibitors have recently been approved in other cancer types such as lung and colorectal cancer.

Patients with RAS-mutated advanced or radioiodine-refractory thyroid cancer who require systemic therapy are typically treated with multikinase inhibitors such as lenvatinib or sorafenib, which work by blocking multiple growth-promoting proteins simultaneously — including targets downstream of RAS — rather than blocking RAS directly. Your oncologist will discuss the systemic therapy options appropriate to your situation.

Clinical trials investigating RAS-targeted approaches in thyroid cancer are ongoing. If your cancer has progressed on standard treatments, asking about clinical trial eligibility is worthwhile.

What happens next

If a RAS mutation was identified in an indeterminate thyroid nodule biopsy, your doctor will likely recommend surgical removal of the nodule — typically a thyroid lobectomy — to obtain the full pathological picture. The final diagnosis and any further treatment decisions will follow the pathology results from surgery.

If a RAS mutation was identified in a confirmed thyroid cancer, your endocrinologist or oncologist will consider this alongside the full molecular profile — particularly TERT promoter mutation status, your tumour type, stage, and other features when planning treatment and follow-up. For most patients with localized fully resected RAS-mutated well-differentiated thyroid cancer, standard management with radioactive iodine (where indicated) and thyroglobulin-based surveillance applies. The combined RAS-plus-TERT finding may warrant a more intensive approach.

If comprehensive molecular profiling has not yet been performed on your thyroid cancer — particularly if you have poorly differentiated thyroid carcinoma, or differentiated thyroid cancer that has spread or stopped responding to radioactive iodine — it is worth asking your oncologist or endocrinologist whether testing is available and appropriate.

Questions to ask your doctor

Which RAS gene was found to be mutated — NRAS, HRAS, or KRAS — and does the specific mutation affect management?
Was TERT promoter mutation testing also performed, and if so, what were the results?
If both a RAS mutation and a TERT promoter mutation are present, how does that combination change my treatment plan or follow-up intensity?
If the RAS result was from an indeterminate nodule biopsy, what is the overall estimated cancer risk, and is surgery recommended?
Were any other molecular alterations identified on the same panel — such as BRAF, RET, or NTRK — that have additional treatment implications?
Does my RAS result affect how my cancer will be monitored after treatment — for example, the type of imaging used for follow-up?
Are there clinical trials I should be aware of that are relevant to RAS-mutated thyroid cancer?