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Endocrinology

Does a RAS gene mutation mean a thyroid lump is cancer?

Medici M, Kwong N, Angell TE, et al. · BMC medicine · 2015

Open access · cc by · source: Europe PMC

Thyroid nodules carrying a RAS mutation turned out to be cancer in fewer than half of cases, and the cancers that were found were all low-risk.

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Study at a glance

Design
Cohort — Prospective blinded cohort at one Boston thyroid clinic: every nodule over 1 cm had FNA cytology plus a 17-alteration mutation panel, interpreted independently of surgical histology; RAS-positive benign nodules were traced back through prior ultrasound records and compared with matched mutation-negative controls.
N
N=362 · 362 nodules from 318 patients after exclusions; 17 nodules were RAS-positive, of which 5 benign nodules had long-term ultrasound follow-up compared with 15 matched mutation-negative controls.
Population
Euthyroid adults referred for ultrasound-guided biopsy of thyroid nodules larger than 1 cm at Brigham and Women's Hospital, 2010-2012.
Outcome
Histological malignancy and cancer features in RAS-positive nodules; nodule growth and cytology over time in RAS-positive benign nodules.

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Key findings

Of 362 nodules, 17 carried a RAS mutation and 8 of these (47%) proved malignant; all 8 were encapsulated follicular-variant papillary cancers with no invasion, spread to lymph nodes or distant metastasis. The other nine RAS-positive nodules were benign, and five followed by ultrasound for a mean of 8.3 years showed no significant growth, whereas matched mutation-negative benign nodules grew by 4.6 mm on average. Patients with benign RAS-positive nodules were about 13 years older than those whose RAS-positive nodules were cancerous. Every cancer was also flagged by abnormal cytology, so the cell test outperformed RAS testing alone.

Methodology

Every adult who came for a biopsy of a thyroid nodule larger than 1 cm between 2010 and 2012 had the usual cell (cytology) test plus a separate gene-mutation panel, with pathologists and lab staff blinded to each other's results. Nodules with suspicious cytology generally went to surgery, while benign ones were watched. For RAS-positive nodules the team recorded surgical pathology and, for benign ones, looked back through years of earlier ultrasound scans and compared growth with age- and sex-matched mutation-negative nodules.

Limitations

Only 17 RAS-positive nodules were found, and just five benign ones had long-term follow-up, so the low-risk conclusion rests on very small numbers and cannot rule out later malignant change. Benign nodules that were not operated on were classed by cytology rather than histology, and the study took place at one institution. It was not designed to test whether mutation testing improves outcomes or is cost-effective, and the authors do not recommend routine RAS testing of all nodules.

How this study connects

Role on claims

Each row is a claim on a concept or method page where this paper supports, challenges, or qualifies the statement. Roles are hand-checked — not a model guess.

  • SupportsThyroid function and health outcomesconcept

    A RAS mutation in a thyroid nodule is not the same as cancer, and the cancers it marks tend to be low-risk.

    In a blinded prospective cohort of 362 biopsied thyroid nodules, only 8 of 17 RAS-positive nodules (47%) were malignant, all were non-invasive encapsulated follicular-variant papillary cancers, and every cancer was also flagged by cytology.

    Evidence for the claim as stated.

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