NRAS mutation in differentiated thyroid cancer

CASE SUMMARY

History and examination

A 46-year-old female patient with no known comorbidities was initially diagnosed with carcinoma thyroid and underwent total thyroidectomy at another facility in 2011. Subsequently, she presented to the head-and-neck Medical Oncology outpatient department at the Tata Memorial Hospital (Mumbai, India) in September 2017. The earlier histopathology report suggested a differentiated variant of follicular thyroid carcinoma. She had undergone radioactive iodine (RAI) ablation twice (193 mCi on April 03, 2012, and 182 mCi on December 20, 2012) in view of iodine-avid foci in the neck and bilateral lungs. At presentation, her Eastern Cooperative Oncology Group (ECOG) performance status was 1 and on clinical examination, a scar from the previous thyroidectomy was present with no palpable lymph nodes.

Investigations and diagnosis

The patient’s post-thyroidectomy slides and blocks were reviewed at our institution. The histopathology report was suggestive of differentiated papillary thyroid carcinoma (follicular variant); lymphovascular invasion was present. She underwent a fluorodeoxyglucose (FDG)-positron emission tomography (PET) scan at another institution in September 2017, which revealed FDG avid sub-cm bilateral lung nodules, largest on the right measuring 1.2 × 1.6 cm (no significant increase in size as compared to those on the previous PET-CT scan done in October 2016) and no FDG uptake at the post-operative site. The patient’s serum thyroid stimulating hormone (TSH) and serum thyroglobulin at presentation were 0.0008 uIU/mL and 161 ng/mL, respectively. She was kept under observation. She received a third dose of RAI 220 mCi in July 2018 (cumulative dose 595 mCi). Her serum thyroglobulin level progressively increased; it was 300 ng/mL in January 2019. A repeat FDG-PET-computed tomography (CT) in February 2019 showed progression in the lung nodules and lytic bone lesions.

Treatment administered

In view of symptomatic RAI-refractory disease, she was started on sorafenib 200 mg orally twice daily in February 2019. She developed grade 3 hand-foot syndrome (HFS) to sorafenib in April 2019. Sorafenib was withheld for 10 days and then restarted at 200 mg once daily. In view of the radiological response in the pulmonary metastasis, a marginal decrease in the 5^th rib lesion, and clinical benefit in bony pain, sorafenib was continued till September 2020. PET-CT scan in September 2020 revealed progressive disease with multiple new lesions (intramuscular, bilateral renal, right adrenal, and liver lesions). She was started on lenvatinib 24 mg orally daily in October 2020. In view of grade 2 HFS, the dose of lenvatinib was reduced to 18 mg orally daily in December 2020. She developed grade 2 HFS on the reduced dose of lenvatinib as well, necessitating a further dose reduction to 14 mg orally daily in March 2021. She developed persistent pleuritic chest pain in January 2022 and the response PET-CT scan showed progression of the disease [Figure 1]. A repeat biopsy of the lung lesion was planned, and she was started on pazopanib 400 mg orally twice a day. She developed grade 3 diarrhea and grade 2 chemotherapy-induced nausea and vomiting (CINV), hence the dose of pazopanib was reduced to 400 mg orally daily. Response PET-CT scan in May 2022 showed progressive disease. She was started on cabozantinib 60 mg orally daily and next-generation sequencing (NGS) was performed on the pre-pazopanib tissue sample. She developed grade 3 HFS on cabozantinib, and hence the dose was reduced to 40 mg orally daily in July 2022. Response PET-CT scan in August 2022 showed progressive disease. The patient was symptomatic for generalized body aches and chest pain. Her ECOG performance status was 2, but her general condition was relatively well-preserved.

Figure 1: Chest CT scan showing pleural based nodule

Next-generation sequencing

Next-generation sequencing (NGS) was carried out on the post-lenvatinib lung biopsy specimen. The panel performed was the Onco-Comprehensive Evaluation for personalized Treatment (OncoCEPT) Solid Panel, which assesses mutations in 52 genes that are considered important in patients with solid tumors. Sequencing was done of the relevant target regions in hotspots and in the entire genes in order to identify single nucleotide variants (SNVs), insertions or deletions (indels), copy number variation (CNVs), and gene fusions. DNA and RNA were analyzed together in a single workflow. The tumor percentage in the formalin-fixed paraffin-embedded (FFPE) block was 40%. With a mean depth of coverage of >250x (DNA), the patient was found to harbor a mutation in exon 3 of the NRAS (Neuroblastoma RAS viral oncogene homolog) gene (c.182A>G p.Gln 61Arg with a variant allele frequency of 14.59%) [Table 1]. The mutation was classified as a Level 3A variation.^[1] No other pathogenic variants were identified in the NGS, including no mutation in BRAF, or KRAS, and no fusions in NTRK, PAX8, ALK, or RET.

Table 1: Details of the next generation sequencing report showing the NRAS mutation

EXCERPTS FROM THE DISCUSSION IN THE MOLECULAR TUMOR BOARD

In our patient with differentiated thyroid cancer, the NRAS mutation was considered pathogenic. However, it was classified as a Level 3A mutation, meaning that there was compelling clinical evidence to support the biomarker as being predictive of response to a drug in this indication. NRAS mutations are frequently encountered in a diverse range of cancers, particularly in melanoma and thyroid carcinomas. The NRAS Q61R mutation has been well-recognized as being oncogenic. As there were no direct NRAS inhibitors commercially available, and as our patient had exhausted standard oral tyrosine kinase inhibitor drugs approved for RAI-refractory differentiated thyroid carcinoma, the molecular tumor board recommended the consideration of trametinib (MEK inhibitor), or in combination with everolimus (mTOR inhibitor) as MEK and mTOR are downstream pathways in the RAS/RAF signaling pathway.

TREATMENT

The patient was explained the current scenario and that all standard lines of therapy were exhausted. The therapeutic options of a MEK inhibitor or the combination of a MEK inhibitor and an mTOR inhibitor were explained, along with a detailed discussion of the cost and associated adverse effects. The patient was started on trametinib 0.5 mg orally daily in Oct 2022, and a month later (Nov 2022), once tolerance to single agent trametinib was assured, everolimus was added at 5 mg orally daily. As of Dec 2022, she continues on the combination of trametinib and everolimus, along with thyroxine 75 mcg daily to maintain the euthyroid status. She is doing well and remains asymptomatic with no notable toxicities.

DISCUSSION

NRAS and mechanism of action

NRAS encodes the guanosine triphosphatase (GTPase) protein, NRAS. It was first identified in human neuroblastoma cells and hence named NRAS. In humans, NRAS is located on chromosome 1: 114.7 – 114.72 Mb.^[2] It was first discovered by Robin Weiss and his team.^[3]

NRAS is a RAS gene family proto-oncogene. The three RAS family genes (HRAS, NRAS, and KRAS) differ in their C-terminal amino acid sequence.^[4] All three RAS genes are involved in the control of normal cell growth.^[5] The NRAS gene produces two main transcripts, a smaller 2 Kb (contains the VIa exon) and a larger 4.3 Kb transcript (contains the VIb exon). Both transcripts encode similar proteins because the only difference between the two is the 3’ untranslated region.

Mutations in NRAS often have changes in 12, 13, or 61 amino acid residues which lead to constitutive activation of NRAS,^[6] thereby transforming a normal cell into a malignant one in a variety of human tumors. NRAS has thus become an important target in the era of precision medicine. The NRAS pathway and various strategies to overcome the activity of mutated NRAS are shown in Figure 2.

Figure 2: NRAS activation pathway and therapeutic targets.GDP: guanosine 5’- diphosphate; GTP: guanosine 5’-triphosphate

NRAS and malignancy

NRAS alterations are seen in 3% of all cancer types. The highest prevalence of NRAS mutations is seen in melanoma, colon carcinoma, acute myeloid leukemia (AML), and lung adenocarcinoma [Figure 3].^[7]

Figure 3: NRAS mutation in various malignancies. Adapted with permission from the AACR Project GENIE^{[ 7 ]}

The commonest alteration in NRAS is a mutation (2.9%), followed by other less common alterations as shown in Figure 4.^[7]

Figure 4: NRAS mutations & frequencies. Adapted with permission from the AACR Project GENIE^{[ 7 ]}

NRAS mutations and thyroid cancer

RAS mutations have been found at various steps of tumorigenesis leading to thyroid cancer, including in adenomas (33%), differentiated follicular carcinomas (53%), and undifferentiated carcinomas (60%).^[8]NRAS mutations are the commonest RAS mutations in thyroid nodules. NRAS is a commonly mutated RAS oncogene (59.4%), and NRAS61 is the most frequent activating point mutation (56.9%).^[9] The NRAS gene is associated with differentiated thyroid cancers as well as a subset of poorly differentiated and anaplastic carcinomas. According to the American Association for Cancer Research (AACR) Project Genomics Evidence Neoplasia Information Exchange (GENIE) Consortium, NRAS alteration is seen in 8.3% of papillary carcinoma, 5.5% of follicular carcinoma, and 19.9% of undifferentiated (anaplastic) carcinoma.^[10]

Prognosis in RAS mutated thyroid cancer

Studies evaluating the prognostic implications of RAS mutations have reported variable results. Earlier, studies reported that RAS mutation-associated thyroid carcinomas are more aggressive.^[10] Some have reported an association between RAS mutations, aggressive biology, and the development of distant metastases. One study with a follow-up period of 35 years showed that about 33% of patients who died of papillary thyroid carcinoma harbored a RAS mutation, whereas only 10.5% of patients who were alive carried it.^[11] However, a retrospective study of 1510 patients demonstrated that RAS-positive tumors had less aggressive histology, less extrathyroidal extension, and lower stage, when compared with BRAF V600E or RET/PTC mutated tumors.^[12] Subsequent studies suggested a strong association between the coexistence of RAS and TERT promoter mutations with late stages, distant metastasis, and recurrence.^[10]

NRAS targeted therapies

NRAS was the first oncogene to be identified in melanoma; NRAS mutation is seen in approximately 20% of melanomas.^[13,14] Various therapeutic strategies have been tried in NRAS-mutated melanomas. Clinical trials of farnesyl transferase inhibitors (lonafarnib and tipifarnib) did not reveal clinical benefits in NRAS- and KRAS-mutated solid tumors.^[15,16] MEK 1/2 inhibitors have been used as they affect the downstream mitogen-activated protein kinase (MAPK) pathway. Seven patients with NRAS-mutated melanoma were included in a Phase I study of trametinib. The best response attained was stable disease in two patients (29%).^[17] In the phase III NEMO trial (binimetinib versus dacarbazine in patients with advanced NRAS-mutant melanoma), binimetinib significantly increased the objective response rate (ORR) (7% versus 15%) and progression-free survival (PFS) (1.5 versus 2.8 months; hazard ratio 0.62 [95% CI, 0.47-0.80]) but there was no difference in overall survival (OS) when compared to dacarbazine.^[18] Compared to dacarbazine, pimasertib (MEK inhibitor) resulted in a median PFS of 13.0 weeks versus 6.9 weeks and a disease control rate (DCR) of 37.7% versus 26.6% but a similar OS (8.9 versus 10.6 months) in a phase II trial of 194 patients with NRAS-mutated cutaneous melanomas.^[19] The combination of alpelisib (a selective PI3Kα inhibitor) and binimetinib in a phase Ib trial of BRAF- or RAS-mutated advanced solid tumors included five patients with NRAS-mutated melanoma. The combination resulted in an ORR of 20% in patients with melanoma.^[20] Pimasertib and voxtalisib (a dual PI3K/mTOR inhibitor) combination in a phase Ib trial showed a response rate of 14% in the melanoma cohort (one complete response and one partial response). The trial was prematurely terminated because of a lack of clinical efficacy and issues with tolerability.^[21]NRAS activation increases cyclin D1 expression and hence regulates downstream cyclin-dependent kinase 4/6 (CDK 4/6). The combination of ribociclib (CDK 4/6 inhibitor) and binimetinib (MEK inhibitor) was evaluated in a phase II study and included 63 patients with NRAS-mutated melanoma. These patients had an ORR of 19.5% (n = 41) and a PFS of 3.7 months (95% CI, 3.5-5.6).^[22]

Patients with NRAS-mutated thyroid cancer have been treated with the MEK inhibitor, trametinib. Iravani and colleagues retrospectively reviewed a re-differentiation protocol attempted in six patients with metastatic RAI-refractory differentiated thyroid cancers harboring driver mutations in BRAF or RAS. Three patients in the cohort had NRAS mutations, including two with follicular thyroid carcinoma, and one with poorly differentiated thyroid carcinoma. Patients with NRAS-mutated tumors were treated with trametinib for 4 weeks. One out of three patients with NRAS-mutated tumors demonstrated RAI uptake and subsequently proceeded to RAI therapy. This patient also had a partial response on imaging beyond 3 months at subsequent follow-ups. Grade 3 acneiform rashes occurred in two patients.^[23]

Table 2 provides the details of trials evaluating various targeted therapies in patients with RAS-mutated differentiated thyroid cancers.

Table 2: Trials in RAS mutated differentiated thyroid carcinomas^{[ 24 ]}

The details of the ongoing trials of MEK inhibitors for thyroid cancer are presented in Table 3.

Table 3: Ongoing trials of MEK inhibitors in thyroid cancer

CONCLUSION

Targeting the downstream signaling pathway in NRAS-mutated thyroid cancer thus represents a type of precision oncology and has the potential to develop targeted therapies. Clinical trials have demonstrated favorable outcomes with MEK inhibitors and other associated MAPK downstream pathway inhibitors in metastatic melanoma in later lines. There are only a few similar trials in thyroid cancer. However, available data show clinically improved outcomes with the use of MEK inhibitors in NRAS-mutated thyroid cancers. MEK inhibitors can also lead to the re-differentiation of RAI-refractory thyroid cancer and RAI-sensitive disease. Thus, large-scale trials with MEK inhibitors in NRAS-mutated thyroid cancer may lead to a significant change in the management paradigms of specific subsets of the disease.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given her consent for images and other clinical information to be reported in the journal. The patient understands that her name and initials will not be published and due efforts will be made to conceal her identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.