A break-apart fluorescence in situ hybridization assay for detecting RET translocations in papillary thyroid carcinoma

RET Proto-Oncogene-Not Such an Obvious Starting Point in Cancer Therapy

Mutations and fusions of RET (rearranged during transfection) gene are detected in a few common types of tumors including thyroid or non-small cells lung cancers. Multiple kinase inhibitors (MKIs) do not show spectacular effectiveness in patients with RET-altered tumors. Hence, recently, two novel RET-specific inhibitors were registered in the US and in Europe. Selpercatinib and pralsetinib showed high efficacy in clinical trials, with fewer adverse effects, in comparison to previously used MKIs. However, the effectiveness of these new drugs may be reduced by the emergence of resistance mutations in RET gene and activation of different activating signaling pathways. This review presents the function of the normal RET receptor, types of molecular disturbances of the RET gene in patients with various cancers, methods of detecting these abnormalities, and the effectiveness of modern anticancer therapies (ranging from immunotherapies, through MKIs, to RET-specific inhibitors).

Diagnostics, therapeutics and RET inhibitor resistance for RET fusion-positive non-small cell lung cancers and future perspectives

Selective RET inhibitors is the current hot topic, making multikinase inhibitors a thing of the past. However, the limitation of various test approaches, coupled with lack of knowledge of acquired resistance mechanisms, and specific patient groups that bear special consideration, remains a challenge. Herein, we outline utility of various diagnostic techniques, provide evidence to guide management of RET-fusion-positive Non-Small Cell Lung Cancer (NSCLC) patients, including specific patient groups, such as EGFR-mutant NSCLC patients who acquired RET fusions after resisting EGFR TKIs, and offer a compendium of mechanisms of acquired resistance to RET targeted therapies. This review further provides a list of ongoing clinical trials and summarizes perspectives to guide future development of drugs and trials for this population.

Progresses Toward Precision Medicine in RET-altered Solid Tumors

RET (rearranged during transfection) gene encodes a receptor tyrosine kinase essential for many physiologic functions, but RET aberrations are involved in many pathologies. While RET loss-of-function mutations are associated with congenital disorders like Hirschsprung disease and CAKUT, RET gain-of-function mutations and rearrangements are critical drivers of tumor growth and proliferation in many different cancers. RET-altered (RET⁺ ) tumors have been hitherto targeted with multikinase inhibitors (MKI) having anti-RET activities, but they inhibit other kinase targets more potently and show limited clinical activities. The lack of target specificity and consequently increased side effects, responsible for dose reduction and drug discontinuation, are critical limitations of MKIs in the clinics. New selective RET inhibitors, selpercatinib and pralsetinib, are showing promising activities, improved response rates, and more favorable toxicity profiles in early clinical trials. This review critically discusses the oncogenic activation of RET and its role in different kinds of tumors, clinical features of RET⁺ tumors, clinically actionable genetic RET alterations and their diagnosis, and the available data and results of nonselective and selective targeting of RET.

Delineating chromosomal breakpoints in radiation-induced papillary thyroid cancer

Recurrent translocations are well known hallmarks of many human solid tumors and hematological disorders, where patient- and breakpoint-specific information may facilitate prognostication and individualized therapy. In thyroid carcinomas, the proto-oncogenes RET and NTRK1 are often found to be activated through chromosomal rearrangements. However, many sporadic tumors and papillary thyroid carcinomas (PTCs) arising in patients with a history of exposure to elevated levels of ionizing irradiation do not carry these known abnormalities. We developed a rapid scheme to screen tumor cell metaphase spreads and identify candidate genes of tumorigenesis and neoplastic progression for subsequent functional studies. Using a series of overnight fluorescence in situ hybridization (FISH) experiments with pools comprised of bacterial artificial chromosome (BAC) clones, it now becomes possible to rapidly refine breakpoint maps and, within one week, progress from the low resolution Spectral Karyotyping (SKY) maps or Giemsa-banding (G-banding) karyotypes to fully integrated, high resolution physical maps including a list of candiate genes in the critical regions.

Kinase expression and chromosomal rearrangements in papillary thyroid cancer tissues: investigations at the molecular and microscopic levels

Structural chromosome aberrations are known hallmarks of many solid tumors. In the papillary form of thyroid cancer (PTC), for example, activation of the receptor tyrosine kinase (RTK) genes, ret or the neurotrophic tyrosine kinase receptor type I (NTRK1) by intra- or interchromosomal rearrangements have been suggested as a cause of the disease. The 1986 accident at the nuclear power plant in Chernobyl, Ukraine, led to the uncontrolled release of high levels of radioisotopes. Ten years later, the incidence of childhood papillary thyroid cancer (chPTC) near Chernobyl had risen by two orders of magnitude. Tumors removed from some of these patients showed aberrant expression of the ret RTK gene due to a ret/PTC1 or ret/PTC3 rearrangement involving chromosome 10. However, many cultured chPTC cells show a normal G-banded karyotype and no ret rearrangement. We hypothesize that the "ret-negative" tumors inappropriately express a different oncogene or have lost function of a tumor suppressor as a result of chromosomal rearrangements, and decided to apply molecular and cytogenetic methods to search for potentially oncogenic chromosomal rearrangements in Chernobyl chPTC cases. Knowledge of the kind of genetic alterations may facilitate the early detection and staging of chPTC as well as provide guidance for therapeutic intervention.