Selpercatinib: First approved selective RET inhibitor.

Selpercatinib is a small molecule that binds at the RET kinase active site. It inhibits activity of constitutively dimerized RET fusion proteins and activated point mutants, thereby blocking downstream signals for proliferation and survival. It is the first selective RET inhibitor to be FDA approved for tumor agnostic targeting of oncogenic RET fusion proteins. To view this Bench to Bedside, open or download the PDF.

First-Line Selpercatinib or Chemotherapy and Pembrolizumab in RET Fusion-Positive NSCLC.

BACKGROUND: Selpercatinib, a highly selective potent and brain-penetrant RET inhibitor, was shown to have efficacy in patients with advanced RET fusion-positive non-small-cell lung cancer (NSCLC) in a nonrandomized phase 1-2 study. METHODS: In a randomized phase 3 trial, we evaluated the efficacy and safety of first-line selpercatinib as compared with control treatment that consisted of platinum-based chemotherapy with or without pembrolizumab at the investigator's discretion. The primary end point was progression-free survival assessed by blinded independent central review in both the intention-to-treat-pembrolizumab population (i.e., patients whose physicians had planned to treat them with pembrolizumab in the event that they were assigned to the control group) and the overall intention-to-treat population. Crossover from the control group to the selpercatinib group was allowed if disease progression as assessed by blinded independent central review occurred during receipt of control treatment. RESULTS: In total, 212 patients underwent randomization in the intention-to-treat-pembrolizumab population. At the time of the preplanned interim efficacy analysis, median progression-free survival was 24.8 months (95% confidence interval [CI], 16.9 to not estimable) with selpercatinib and 11.2 months (95% CI, 8.8 to 16.8) with control treatment (hazard ratio for progression or death, 0.46; 95% CI, 0.31 to 0.70; P<0.001). The percentage of patients with an objective response was 84% (95% CI, 76 to 90) with selpercatinib and 65% (95% CI, 54 to 75) with control treatment. The cause-specific hazard ratio for the time to progression affecting the central nervous system was 0.28 (95% CI, 0.12 to 0.68). Efficacy results in the overall intention-to-treat population (261 patients) were similar to those in the intention-to-treat-pembrolizumab population. The adverse events that occurred with selpercatinib and control treatment were consistent with those previously reported. CONCLUSIONS: Treatment with selpercatinib led to significantly longer progression-free survival than platinum-based chemotherapy with or without pembrolizumab among patients with advanced RET fusion-positive NSCLC. (Funded by Eli Lilly and others; ClinicalTrials.gov number, NCT04194944.).

Patient with mediastinal carcinoma of unknown primary with RET fusion achieves durable response with RET inhibition.

Selective RET inhibitors have shown promise in thyroid cancer (TC) and nonsmall cell lung cancer (NSCLC) harboring RET fusions on next-generation sequencing (NGS), although rarity of the rearrangement has led to limited data for certain tumor types, such as carcinoma of unknown primary. We present a 65-year-old female with no history of malignancy, smoking or radiation exposure, who was found to have an anterior mediastinum malignancy of unknown primary, with metastases to supraclavicular lymph nodes. Core biopsy of the mediastinum revealed poorly differentiated carcinoma, while a biopsy of the thyroid revealed atypia of indeterminate significance (Bethesda III). PD-L1 immunohistochemistry was positive (90%), and liquid NGS revealed mutations in TP53 and the TERT promoter (c.-124C>T), as well as a CCDC6-RET fusion. This genetic profile resembled an anaplastic TC vs. NSCLC primary, although thymic primary and poorly differentiated TC remained on the differential. The patient was initiated on selpercatinib, which was held after 3 weeks due to thrombocytopenia and hypertension. At a reduced dosage, patient developed transaminitis, and selpercatinib was switched to pralsetinib. Brain MRI showed a nonenhancing temporal lobe signal abnormality, which on biopsy proved to be glioblastoma (GBM) with TERT promoter c.-124C>T mutation and FGFR3-TACC3 fusion by NGS. Pralsetinib was held during adjuvant chemoradiation for the GBM, and again for 4 weeks due to pneumonitis that resolved with steroids, and pralsetinib was restarted at a reduced dose. The patient has since demonstrated a stable reduction of the mediastinal mass for >15 months with RET inhibition therapy, despite several treatment interruptions.

Discovery of 9H-pyrimido[4,5-b]indole derivatives as dual RET/TRKA inhibitors.

Aberrant RET kinase signaling is activated in numerous cancers including lung, thyroid, breast, pancreatic, and prostate. Recent approvals of selective RET inhibitors, pralsetinib and selpercatinib, has shifted the focus of RET kinase drug discovery programs towards the development of selective inhibitors. However, selective inhibitors invariably lose efficacy as the selective nature of the inhibitor places Darwinian-like pressure on the tumor to bypass treatment through the selection of novel oncogenic drivers. Further, selective inhibitors are restricted for use in tumors with specific genetic backgrounds that do not encompass diverse patient classes. Here we report the identification of a pyrimido indole RET inhibitor found to also have activity against TRK. This selective dual RET/TRK inhibitor can be utilized in tumors with both RET and TRK genetic backgrounds and can also provide blockade of NTRK-fusions that are selected for from RET inhibitor treatments. Efforts towards developing dual RET/TRK inhibitors can be beneficial in terms of encompassing more diverse patient classes while also achieving blockade against emerging resistance mechanisms.

Generating Potential RET-Specific Inhibitors Using a Novel LSTM Encoder-Decoder Model.

The receptor tyrosine kinase RET (rearranged during transfection) plays a vital role in various cell signaling pathways and is a critical factor in the development of the nervous system. Abnormal activation of the RET kinase can lead to several cancers, including thyroid cancer and non-small-cell lung cancer. However, most RET kinase inhibitors are multi-kinase inhibitors. Therefore, the development of an effective RET-specific inhibitor continues to present a significant challenge. To address this issue, we built a molecular generation model based on fragment-based drug design (FBDD) and a long short-term memory (LSTM) encoder-decoder structure to generate receptor-specific molecules with novel scaffolds. Remarkably, our model was trained with a molecular assembly accuracy of 98.4%. Leveraging the pre-trained model, we rapidly generated a RET-specific-candidate active-molecule library by transfer learning. Virtual screening based on our molecular generation model was performed, combined with molecular dynamics simulation and binding energy calculation, to discover specific RET inhibitors, and five novel molecules were selected. Further analyses indicated that two of these molecules have good binding affinities and synthesizability, exhibiting high selectivity. Overall, this investigation demonstrates the capacity of our model to generate novel receptor-specific molecules and provides a rapid method to discover potential drugs.

Efficacy of Selpercatinib in RET Fusion-Positive Non-Small-Cell Lung Cancer.

BACKGROUND: RET fusions are oncogenic drivers in 1 to 2% of non-small-cell lung cancers (NSCLCs). In patients with RET fusion-positive NSCLC, the efficacy and safety of selective RET inhibition are unknown. METHODS: We enrolled patients with advanced RET fusion-positive NSCLC who had previously received platinum-based chemotherapy and those who were previously untreated separately in a phase 1-2 trial of selpercatinib. The primary end point was an objective response (a complete or partial response) as determined by an independent review committee. Secondary end points included the duration of response, progression-free survival, and safety. RESULTS: In the first 105 consecutively enrolled patients with RET fusion-positive NSCLC who had previously received at least platinum-based chemotherapy, the percentage with an objective response was 64% (95% confidence interval [CI], 54 to 73). The median duration of response was 17.5 months (95% CI, 12.0 to could not be evaluated), and 63% of the responses were ongoing at a median follow-up of 12.1 months. Among 39 previously untreated patients, the percentage with an objective response was 85% (95% CI, 70 to 94), and 90% of the responses were ongoing at 6 months. Among 11 patients with measurable central nervous system metastasis at enrollment, the percentage with an objective intracranial response was 91% (95% CI, 59 to 100). The most common adverse events of grade 3 or higher were hypertension (in 14% of the patients), an increased alanine aminotransferase level (in 12%), an increased aspartate aminotransferase level (in 10%), hyponatremia (in 6%), and lymphopenia (in 6%). A total of 12 of 531 patients (2%) discontinued selpercatinib because of a drug-related adverse event. CONCLUSIONS: Selpercatinib had durable efficacy, including intracranial activity, with mainly low-grade toxic effects in patients with RET fusion-positive NSCLC who had previously received platinum-based chemotherapy and those who were previously untreated. (Funded by Loxo Oncology and others; LIBRETTO-001 ClinicalTrials.gov number, NCT03157128.).

Efficacy of Selpercatinib in RET-Altered Thyroid Cancers.

BACKGROUND: RET mutations occur in 70% of medullary thyroid cancers, and RET fusions occur rarely in other thyroid cancers. In patients with RET-altered thyroid cancers, the efficacy and safety of selective RET inhibition are unknown. METHODS: We enrolled patients with RET-mutant medullary thyroid cancer with or without previous vandetanib or cabozantinib treatment, as well as those with previously treated RET fusion-positive thyroid cancer, in a phase 1-2 trial of selpercatinib. The primary end point was an objective response (a complete or partial response), as determined by an independent review committee. Secondary end points included the duration of response, progression-free survival, and safety. RESULTS: In the first 55 consecutively enrolled patients with RET-mutant medullary thyroid cancer who had previously received vandetanib, cabozantinib, or both, the percentage who had a response was 69% (95% confidence interval [CI], 55 to 81), and 1-year progression-free survival was 82% (95% CI, 69 to 90). In 88 patients with RET-mutant medullary thyroid cancer who had not previously received vandetanib or cabozantinib, the percentage who had a response was 73% (95% CI, 62 to 82), and 1-year progression-free survival was 92% (95% CI, 82 to 97). In 19 patients with previously treated RET fusion-positive thyroid cancer, the percentage who had a response was 79% (95% CI, 54 to 94), and 1-year progression-free survival was 64% (95% CI, 37 to 82). The most common adverse events of grade 3 or higher were hypertension (in 21% of the patients), increased alanine aminotransferase level (in 11%), increased aspartate aminotransferase level (in 9%), hyponatremia (in 8%), and diarrhea (in 6%). Of all 531 patients treated, 12 (2%) discontinued selpercatinib owing to drug-related adverse events. CONCLUSIONS: In this phase 1-2 trial, selpercatinib showed durable efficacy with mainly low-grade toxic effects in patients with medullary thyroid cancer with and without previous vandetanib or cabozantinib treatment. (Funded by Loxo Oncology and others; LIBRETTO-001 ClinicalTrials.gov number, NCT03157128.).

Hypertension and Prohypertensive Antineoplastic Therapies in Cancer Patients.

The development of a wide range of novel antineoplastic therapies has improved the prognosis for patients with a wide range of malignancies, which has increased the number of cancer survivors substantially. Despite the oncological benefit, cancer survivors are exposed to short- and long-term adverse cardiovascular toxicities associated with anticancer therapies. Systemic hypertension, the most common comorbidity among cancer patients, is a major contributor to the increased risk for developing these adverse cardiovascular events. Cancer and hypertension have common risk factors, have overlapping pathophysiological mechanisms and hypertension may also be a risk factor for some tumor types. Many cancer therapies have prohypertensive effects. Although some of the mechanisms by which these antineoplastic agents lead to hypertension have been characterized, further preclinical and clinical studies are required to investigate the exact pathophysiology and the optimal management of hypertension associated with anticancer therapy. In this way, monitoring and management of hypertension before, during, and after cancer treatment can be improved to minimize cardiovascular risks. This is vital to optimize cardiovascular health in patients with cancer and survivors, and to ensure that advances in terms of cancer survivorship do not come at the expense of increased cardiovascular toxicities.

Crowdsourced identification of multi-target kinase inhibitors for RET- and TAU- based disease: The Multi-Targeting Drug DREAM Challenge.

A continuing challenge in modern medicine is the identification of safer and more efficacious drugs. Precision therapeutics, which have one molecular target, have been long promised to be safer and more effective than traditional therapies. This approach has proven to be challenging for multiple reasons including lack of efficacy, rapidly acquired drug resistance, and narrow patient eligibility criteria. An alternative approach is the development of drugs that address the overall disease network by targeting multiple biological targets ('polypharmacology'). Rational development of these molecules will require improved methods for predicting single chemical structures that target multiple drug targets. To address this need, we developed the Multi-Targeting Drug DREAM Challenge, in which we challenged participants to predict single chemical entities that target pro-targets but avoid anti-targets for two unrelated diseases: RET-based tumors and a common form of inherited Tauopathy. Here, we report the results of this DREAM Challenge and the development of two neural network-based machine learning approaches that were applied to the challenge of rational polypharmacology. Together, these platforms provide a potentially useful first step towards developing lead therapeutic compounds that address disease complexity through rational polypharmacology.

Pralsetinib for RET fusion-positive non-small-cell lung cancer (ARROW): a multi-cohort, open-label, phase 1/2 study.

BACKGROUND: Oncogenic alterations in RET have been identified in multiple tumour types, including 1-2% of non-small-cell lung cancers (NSCLCs). We aimed to assess the safety, tolerability, and antitumour activity of pralsetinib, a highly potent, oral, selective RET inhibitor, in patients with RET fusion-positive NSCLC. METHODS: ARROW is a multi-cohort, open-label, phase 1/2 study done at 71 sites (community and academic cancer centres) in 13 countries (Belgium, China, France, Germany, Hong Kong, Italy, Netherlands, Singapore, South Korea, Spain, Taiwan, the UK, and the USA). Patients aged 18 years or older with locally advanced or metastatic solid tumours, including RET fusion-positive NSCLC, and an Eastern Cooperative Oncology Group performance status of 0-2 (later limited to 0-1 in a protocol amendment) were enrolled. In phase 2, patients received 400 mg once-daily oral pralsetinib, and could continue treatment until disease progression, intolerance, withdrawal of consent, or investigator decision. Phase 2 primary endpoints were overall response rate (according to Response Evaluation Criteria in Solid Tumours version 1·1 and assessed by blinded independent central review) and safety. Tumour response was assessed in patients with RET fusion-positive NSCLC and centrally adjudicated baseline measurable disease who had received platinum-based chemotherapy or were treatment-naive because they were ineligible for standard therapy. This ongoing study is registered with ClinicalTrials.gov, NCT03037385, and enrolment of patients with treatment-naive RET fusion-positive NSCLC was ongoing at the time of this interim analysis. FINDINGS: Of 233 patients with RET fusion-positive NSCLC enrolled between March 17, 2017, and May 22, 2020 (data cutoff), 92 with previous platinum-based chemotherapy and 29 who were treatment-naive received pralsetinib before July 11, 2019 (efficacy enrolment cutoff); 87 previously treated patients and 27 treatment-naive patients had centrally adjudicated baseline measurable disease. Overall responses were recorded in 53 (61%; 95% CI 50-71) of 87 patients with previous platinum-based chemotherapy, including five (6%) patients with a complete response; and 19 (70%; 50-86) of 27 treatment-naive patients, including three (11%) with a complete response. In 233 patients with RET fusion-positive NSCLC, common grade 3 or worse treatment-related adverse events were neutropenia (43 patients [18%]), hypertension (26 [11%]), and anaemia (24 [10%]); there were no treatment-related deaths in this population. INTERPRETATION: Pralsetinib is a new, well-tolerated, promising, once-daily oral treatment option for patients with RET fusion-positive NSCLC. FUNDING: Blueprint Medicines.

Novel Human-Derived RET Fusion NSCLC Cell Lines Have Heterogeneous Responses to RET Inhibitors and Differential Regulation of Downstream Signaling.

Rearranged during transfection (RET) rearrangements occur in 1% to 2% of lung adenocarcinomas as well as other malignancies and are now established targets for tyrosine kinase inhibitors. We developed three novel RET fusion-positive (RET+) patient-derived cancer cell lines, CUTO22 [kinesin 5B (KIF5B)-RET fusion], CUTO32 (KIF5B-RET fusion), and CUTO42 (echinoderm microtubule-associated protein-like 4-RET fusion), to study RET signaling and response to therapy. We confirmed each of our cell lines expresses the RET fusion protein and assessed their sensitivity to RET inhibitors. We found that the CUTO22 and CUTO42 cell lines were sensitive to multiple RET inhibitors, whereas the CUTO32 cell line was >10-fold more resistant to three RET inhibitors. We discovered that our RET+ cell lines had differential regulation of the mitogen-activated protein kinase and phosphoinositide 3-kinase/protein kinase B (AKT) pathways. After inhibition of RET, the CUTO42 cells had robust inhibition of phosphorylated AKT (pAKT), whereas CUTO22 and CUTO32 cells had sustained AKT activation. Next, we performed a drug screen, which revealed that the CUTO32 cells were sensitive (<1 nM IC50) to inhibition of two cell cycle-regulating proteins, polo-like kinase 1 and Aurora kinase A. Finally, we show that two of these cell lines, CUTO32 and CUTO42, successfully establish xenografted tumors in nude mice. We demonstrated that the RET inhibitor BLU-667 was effective at inhibiting tumor growth in CUTO42 tumors but had a much less profound effect in CUTO32 tumors, consistent with our in vitro experiments. These data highlight the utility of new RET+ models to elucidate differences in response to tyrosine kinase inhibitors and downstream signaling regulation. Our RET+ cell lines effectively recapitulate the interpatient heterogeneity observed in response to RET inhibitors and reveal opportunities for alternative or combination therapies. SIGNIFICANCE STATEMENT: We have derived and characterized three novel rearranged during transfection (RET) fusion non-small cell lung cancer cell lines and demonstrated that they have differential responses to RET inhibition as well as regulation of downstream signaling, an area that has previously been limited by a lack of diverse cell line modes with endogenous RET fusions. These data offer important insight into regulation of response to RET tyrosine kinase inhibitors and other potential therapeutic targets.

An early look at selective RET inhibitor resistance: new challenges and opportunities.

Two RET inhibitors, selpercatinib and pralsetinib, recently received approval for the treatment of advanced RET fusion-positive lung cancer. Acquired resistance to these inhibitors will be a major challenge. We have shown that resistance can emerge due to recurrent RET kinase domain mutations and, in most cases, due to RET-independent mechanisms.

ABCB1 and ABCG2, but not CYP3A4 limit oral availability and brain accumulation of the RET inhibitor pralsetinib.

BACKGROUND AND PURPOSE: Pralsetinib is an FDA-approved oral small-molecule inhibitor for treatment of rearranged during transfection (RET) proto-oncogene fusion-positive non-small cell lung cancer. We investigated how the efflux transporters ABCB1 and ABCG2, the SLCO1A/1B uptake transporters and the drug-metabolizing enzyme CYP3A influence pralsetinib pharmacokinetics. EXPERIMENTAL APPROACH: In vitro, transepithelial pralsetinib transport was assessed. In vivo, pralsetinib (10 mg/kg) was administered orally to relevant genetically modified mouse models. Pralsetinib concentrations in cell medium, plasma samples and organ homogenates were measured using liquid chromatography-tandem mass spectrometry. KEY RESULTS: Pralsetinib was efficiently transported by human (h)ABCB1 and mouse (m)Abcg2, but not hACBG2. In vivo, mAbcb1a/1b markedly and mAbcg2 slightly limited pralsetinib brain penetration (6.3-and 1.8-fold, respectively). Testis distribution showed similar results. Abcb1a/1b;Abcg2-/- mice showed 1.5-fold higher plasma exposure, 23-fold increased brain penetration, and 4-fold reduced recovery of pralsetinib in the small intestinal content. mSlco1a/1b deficiency did not affect pralsetinib oral availability or tissue exposure. Oral coadministration of the ABCB1/ABCG2 inhibitor elacridar boosted pralsetinib plasma exposure (1.3-fold) and brain penetration (19.6-fold) in wild-type mice. Additionally, pralsetinib was a modest substrate of mCYP3A, but not of hCYP3A4, which did not noticeably restrict the oral availability or tissue distribution of pralsetinib. CONCLUSIONS AND IMPLICATIONS: SLCO1A/1B and CYP3A4 are unlikely to affect the pharmacokinetics of pralsetinib, but ABCG2 and especially ABCB1 markedly limit its brain and testis penetration, as well as oral availability. These effects are mostly reversed by oral coadministration of the ABCB1/ABCG2 inhibitor elacridar. These insights may be useful in the further clinical development of pralsetinib.

Discovery and optimization of selective RET inhibitors via scaffold hopping.

Aberrant alterations of rearranged during transfection (RET) have been identified as actionable drivers of multiple cancers, including thyroid carcinoma and lung cancer. Currently, several approved multikinase inhibitors such as vandetanib and cabozantinib demonstrate clinical activity in patients with RET-rearranged or RET-mutant cancers. However, the observed response rates are only modest and the 'off-target' toxicities resulted from the inhibition of other kinases is also a concern. Herein, we designed and synthesized a series of RET inhibitors based on the structure of selective RET inhibitor BLU-667 and investigated their biological activities. We identified compound 9 as a novel potent and selective RET inhibitor with improved drug-like properties. Compound 9 exhibits a selective inhibitory profile with an inhibitory concentration 50 (IC50) of 1.29 nM for RET and 1.97 (RET V804M) or 0.99 (RET M918T) for mutant RETs. The proliferation of Ba/F3 cells transformed with NSCLC related KIF5B-RET fusion was effectively suppressed by compound 9 (IC50 = 19 nM). Additionally, compound 9 displayed less 'off-target' effects than BLU-667. In mouse xenograft models, compound 9 repressed tumor growth driven by KIF5B-RET-Ba/F3 cells in a dose-dependent manner. Based on its exceptional kinase selectivity, good potency and high exposure in tumor tissues, compound 9 represents a promising lead for the discovery of RET directed therapeutic agents and the study of RET-driven tumor biology.

Therapeutic Advances in the Management of Patients with Advanced RET Fusion-Positive Non-Small Cell Lung Cancer.

OPINION STATEMENT: Screening for activating driver gene alterations at the time of diagnosis is the standard of care for advanced non-small cell lung cancer (NSCLC). Activating RET fusions are identified in approximately 1-2% of NSCLCs and have emerged as a targetable driver alteration. Selpercatinib and pralsetinib are RET-selective tyrosine kinase inhibitors (TKIs) with encouraging efficacy, intracranial activity, and tolerability that we recommend as first-line therapy. As with use of TKIs in other oncogene-addicted NSCLCs, development of acquired resistance is pervasive and should be specifically delineated through use of repeat tissue biopsy with genetic profiling at the time of disease progression. If an actionable resistance mechanism emerges for which there is a candidate targeted therapy, combination inhibition should be considered. Alternatively, or in the absence of such findings, platinum doublet chemotherapy or particularly platinum-pemetrexed therapy with or without bevacizumab demonstrates a moderate effect.We would not recommend the routine use of nonselective multi-targeted TKIs such as cabozantinib and vandetanib, which have modest activity but limited tolerability due to predictable off-target effects. Single-agent immunotherapy has minimal activity in RET fusion-positive NSCLC. The role of combination chemotherapy and immunotherapy requires further study but may be considered, particularly in the presence of an activating KRAS alteration. While further development of novel RET-selective TKIs may address common RET-specific resistance mutations, they will not have activity against off-target, RET-independent resistance mechanisms. This again highlights the importance of serial biopsy and next-generation sequencing for the rational choice of sequential therapy in RET fusion-positive NSCLC.

Determination of selpercatinib, a RET kinase inhibitor, in rat plasma and its application to a pharmacokinetic study.

Selpercatinib (LOXO-292) is a selective and potent RET inhibitor. A highly sensitive, rapid and specific high-performance liquid chromatography with tandem mass spectrometry (LC-MS/MS) method for quantification of selpercatinib in rat plasma is reported. The method was validated in terms of selectivity, linearity, accuracy and precision, extraction recovery and matrix effect, stability and carryover as per the US Food and Drug Administration guidelines for bioanalytical method validation. Selpercatinib was detected by an electrospray ionization interface under selective reaction monitoring conditions in the positive ion mode. The calibration curve was linear over the concentration range from 1 to 2000 ng/ml with r2 = 0.9951. The intra- and inter-batch accuracy values ranged from 97.45 to 100.97% and from 98.70 to 100.74% with coefficients of variation of 2.45-6.99% and 5.89-7.99%, respectively. The extraction recovery and IS-normalized matrix factor were acceptable for the bioanalysis of selpercatinib. Additionally, selpercatinib was found to be stable under the detected conditions. It showed linear pharmacokinetic characteristics following oral administration to rats at 2.0-18.0 mg/kg. The results showed that the novel method for detecting selpercatinib in rat plasma could be successfully applied for quantification of selpercatinib in biosamples from nonclinical studies.

REToma: a cancer subtype with a shared driver oncogene.

RET (REarranged during Transfection), which encodes a receptor tyrosine kinase for members of the glial cell line-derived neurotrophic factor, plays a role as driver oncogene in a variety of human cancers. Fusion of RET with several partner genes has been detected in papillary thyroid, lung, colorectal, pancreatic and breast cancers, and tyrosine kinase inhibitors (TKIs) for RET (particularly RET-specific inhibitors) show promising therapeutic effects against such cancers. Oncogenic mutations within the extracellular cysteine-rich and intracellular kinase domains of RET drive medullary thyroid carcinogenesis; the same mutations are also observed in a small subset of diverse cancers such as lung, colorectal and breast cancers. Considering the oncogenic nature of RET mutants, lung, colorectal and breast cancers are predicted to respond to RET TKIs in a manner similar to medullary thyroid cancer. In summary, cancers carrying oncogenic RET alterations as a driver mutation could be collectively termed 'REToma' and treated with RET TKIs in a tissue-agnostic manner.

Update on the Treatment of Medullary Thyroid Carcinoma in Patients with Multiple Endocrine Neoplasia Type 2.

Medullary Thyroid Carcinoma (MTC) is a rare neuroendocrine cancer that accounts for 1-2% of thyroid cancers in the United States (U.S.). While most cases are sporadic, 25% of MTC cases are hereditary. These hereditary cases occur in the setting of Multiple Endocrine Neoplasia Type 2A (MEN2A) or 2B (MEN2B) driven by mutations in the Rearranged during Transfection RET proto-oncogene. This article discusses hereditary MTC in the setting of MEN2 and the treatment options available for it. The first line treatment for this disease is typically a total thyroidectomy and tyrosine kinase inhibitors. Two tyrosine kinase inhibitors, vandetanib and cabozantinib, have been approved for treatment of advanced MTC, but options beyond those are limited. However, several promising treatments are being studied, which are discussed in this review.