Sirolimus therapy for fibromatosis and multifocal renal cell carcinoma in a child with tuberous sclerosis complex

Rapamycin and rapalogs for tuberous sclerosis complex

BACKGROUND

Potential benefits of rapamycin or rapalogs for treating people with tuberous sclerosis complex (TSC) have been shown. Currently everolimus (a rapalog) is only approved for TSC-associated renal angiomyolipoma and subependymal giant cell astrocytoma (SEGA), but not other manifestations of TSC. A systematic review needs to establish evidence for rapamycin or rapalogs for various manifestations in TSC. This is an updated review.

OBJECTIVES

To determine the effectiveness of rapamycin or rapalogs in people with TSC for decreasing tumour size and other manifestations and to assess the safety of rapamycin or rapalogs in relation to their adverse effects.

SEARCH METHODS

We identified relevant studies from the Cochrane-Central-Register-of-Controlled-Trials (CENTRAL), Ovid MEDLINE and ongoing trials registries with no language restrictions. We searched conference proceedings and abstract books of conferences. Date of the last searches: 15 July 2022.

SELECTION CRITERIA

Randomised controlled trials (RCTs) or quasi-RCTs of rapamycin or rapalogs in people with TSC.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data and assessed the risk of bias of each study; a third review author verified the extracted data and risk of bias decisions. We assessed the certainty of the evidence using GRADE.

MAIN RESULTS

The current update added seven RCTs, bringing the total number to 10 RCTs (with 1008 participants aged 3 months to 65 years; 484 males). All TSC diagnoses were by consensus criteria as a minimum. In parallel studies, 645 participants received active interventions and 340 placebo. Evidence is low-to-high certainty and study quality is mixed; mostly a low risk of bias across domains, but one study had a high risk of performance bias (lack of blinding) and three studies had a high risk of attrition bias. Manufacturers of the investigational products supported eight studies. Systemic administration Six studies (703 participants) administered everolimus (rapalog) orally. More participants in the intervention arm reduced renal angiomyolipoma size by 50% (risk ratio (RR) 24.69, 95% confidence interval (CI) 3.51 to 173.41; P = 0.001; 2 studies, 162 participants, high-certainty evidence). In the intervention arm, more participants in the intervention arm reduced SEGA tumour size by 50% (RR 27.85, 95% CI 1.74 to 444.82; P = 0.02; 1 study; 117 participants; moderate-certainty evidence) ,and reported more skin responses (RR 5.78, 95% CI 2.30 to 14.52; P = 0.0002; 2 studies; 224 participants; high-certainty evidence). In one 18-week study (366 participants), the intervention led to 25% fewer seizures (RR 1.63, 95% CI 1.27 to 2.09; P = 0.0001) or 50% fewer seizures (RR 2.28, 95% CI 1.44 to 3.60; P = 0.0004); but there was no difference in numbers being seizure-free (RR 5.30, 95% CI 0.69 to 40.57; P = 0.11) (moderate-certainty evidence). One study (42 participants) showed no difference in neurocognitive, neuropsychiatry, behavioural, sensory and motor development (low-certainty evidence). Total adverse events (AEs) did not differ between groups (RR 1.09, 95% CI 0.97 to 1.22; P = 0.16; 5 studies; 680 participants; high-certainty evidence). However, the intervention group experienced more AEs resulting in withdrawal, interruption of treatment, or reduced dose (RR 2.61, 95% CI 1.58 to 4.33; P = 0.0002; 4 studies; 633 participants; high-certainty evidence and also reported more severe AEs (RR 2.35, 95% CI 0.99 to 5.58; P = 0.05; 2 studies; 413 participants; high-certainty evidence). Topical (skin) administration Four studies (305 participants) administered rapamycin topically. More participants in the intervention arm showed a response to skin lesions (RR 2.72, 95% CI 1.76 to 4.18; P < 0.00001; 2 studies; 187 participants; high-certainty evidence) and more participants in the placebo arm reported a deterioration of skin lesions (RR 0.27, 95% CI 0.15 to 0.49; 1 study; 164 participants; high-certainty evidence). More participants in the intervention arm responded to facial angiofibroma at one to three months (RR 28.74, 95% CI 1.78 to 463.19; P = 0.02) and three to six months (RR 39.39, 95% CI 2.48 to 626.00; P = 0.009; low-certainty evidence). Similar results were noted for cephalic plaques at one to three months (RR 10.93, 95% CI 0.64 to 186.08; P = 0.10) and three to six months (RR 7.38, 95% CI 1.01 to 53.83; P = 0.05; low-certainty evidence). More participants on placebo showed a deterioration of skin lesions (RR 0.27, 95% CI 0.15 to 0.49; P < 0.0001; 1 study; 164 participants; moderate-certainty evidence). The intervention arm reported a higher general improvement score (MD -1.01, 95% CI -1.68 to -0.34; P < 0.0001), but no difference specifically in the adult subgroup (MD -0.75, 95% CI -1.58 to 0.08; P = 0.08; 1 study; 36 participants; moderate-certainty evidence). Participants in the intervention arm reported higher satisfaction than with placebo (MD -0.92, 95% CI -1.79 to -0.05; P = 0.04; 1 study; 36 participants; low-certainty evidence), although again with no difference among adults (MD -0.25, 95% CI -1.52 to 1.02; P = 0.70; 1 study; 18 participants; low-certainty evidence). Groups did not differ in change in quality of life at six months (MD 0.30, 95% CI -1.01 to 1.61; P = 0.65; 1 study; 62 participants; low-certainty evidence). Treatment led to a higher risk of any AE compared to placebo (RR 1.72, 95% CI 1.10, 2.67; P = 0.02; 3 studies; 277 participants; moderate-certainty evidence); but no difference between groups in severe AEs (RR 0.78, 95% CI 0.19 to 3.15; P = 0.73; 1 study; 179 participants; moderate-certainty evidence).

AUTHORS' CONCLUSIONS

Oral everolimus reduces the size of SEGA and renal angiomyolipoma by 50%, reduces seizure frequency by 25% and 50% and implements beneficial effects on skin lesions with no difference in the total number of AEs compared to placebo; however, more participants in the treatment group required a dose reduction, interruption or withdrawal and marginally more experienced serious AEs compared to placebo. Topical rapamycin increases the response to skin lesions and facial angiofibroma, an improvement score, satisfaction and the risk of any AE, but not severe adverse events. With caution regarding the risk of severe AEs, this review supports oral everolimus for renal angiomyolipoma, SEGA, seizure, and skin lesions, and topical rapamycin for facial angiofibroma.

Tumorigenesis Mechanisms Found in Hereditary Renal Cell Carcinoma: A Review

Renal cell carcinoma is a heterogenous cancer composed of an increasing number of unique subtypes each with their own cellular and tumor behavior. The study of hereditary renal cell carcinoma, which composes just 5% of all types of tumor cases, has allowed for the elucidation of subtype-specific tumorigenesis mechanisms that can also be applied to their sporadic counterparts. This review will focus on the major forms of hereditary renal cell carcinoma and the genetic alterations contributing to their tumorigenesis, including von Hippel Lindau syndrome, Hereditary Papillary Renal Cell Carcinoma, Succinate Dehydrogenase-Deficient Renal Cell Carcinoma, Hereditary Leiomyomatosis and Renal Cell Carcinoma, BRCA Associated Protein 1 Tumor Predisposition Syndrome, Tuberous Sclerosis, Birt-Hogg-Dubé Syndrome and Translocation RCC. The mechanisms for tumorigenesis described in this review are beginning to be exploited via the utilization of novel targets to treat renal cell carcinoma in a subtype-specific fashion.

Bilateral Renal Tumors in Children: The First 5 Years' Experience of National Centralization in The Netherlands and a Narrative Review of the Literature

Survival of unilateral Wilms tumors (WTs) is exceeding 90%, whereas bilateral WTs have an inferior outcome. We evaluated all Dutch patients with bilateral kidney tumors, treated in the first five years of national centralization and reviewed relevant literature. We identified 24 patients in our center (2015–2020), 23 patients had WT/nephroblastomatosis and one renal cell carcinoma. Patients were treated according to SIOP-RTSG protocols. Chemotherapy response was observed in 26/34 WTs. Nephroblastomatosis lesions were stable (n = 7) or showed response (n = 18). Nephron-sparing surgery was performed in 11/22 patients undergoing surgery (n = 2 kidneys positive margins). Local stage in 20 patients with ≥1 WT revealed stage I (n = 7), II (n = 4) and III (n = 9). Histology was intermediate risk in 15 patients and high risk in 5. Three patients developed a WT in a treated nephroblastomatosis lesion. Two of 24 patients died following toxicity and renal failure, i.e., respectively dialysis-related invasive fungal infection and septic shock. Genetic predisposition was confirmed in 18/24 patients. Our literature review revealed that knowledge is scarce on bilateral renal tumor patients with metastases and that radiotherapy seems important for local stage III patients. Bilateral renal tumors are a therapeutic challenge. We describe management and outcome in a national expert center and summarized available literature, serving as baseline for further improvement of care.

Pediatric and young adult renal cell carcinoma

Renal cell carcinoma (RCC) is rare in children but is the most common renal tumor in adults. Pediatric RCC has different clinical characteristics, histopathology, and treatment compared with adult disease. Databases were reviewed from inception to February 2020, identifying 32 publications pertaining to 350 patients under 27 years. Surgery is the cornerstone for cure in localized RCC. Lymph node dissection remains controversial. Conventional radiotherapy has no curative role in RCC; similarly, conventional chemotherapy has not proven to be effective in large cohorts. Pediatric metastatic RCC has a poor outlook. There are no published prospective studies demonstrating which adjuvant therapy could improve outcome. Sunitinib, a tyrosine kinase inhibitor, is recommended in this group despite limited evidence. This review provides an overview for pediatric RCC, including the evolving role of precision medicine.

[Mesenchymal abdominal tumors in children]

Mesenchymal tumors in childhood comprise benign and malign entities and differ regarding typical sites of manifestation, age peak and clinical symptoms. In some cases biopsy is mandatory. If nephroblastoma is a possible diagnosis, biopsy must be avoided by all means in order to avoid biopsy tract metastasis. Imaging is used to narrow the differential diagnosis, describe the exact extent of the lesion and deliver complete staging. In pediatric patients sonography and MRI are the most important imaging modalities. Low-dose CT of the thorax serves for assessment of possible pulmonary metastases.

Exceptional response to everolimus in a novel tuberous sclerosis complex-2 mutation-associated metastatic renal-cell carcinoma

Everolimus, an oral inhibitor of the mammalian target of rapamycin (mTOR) pathway, is currently approved for treatment of advanced renal-cell carcinoma (RCC) after failure of initial treatment with the tyrosine kinase inhibitors. Patients with tuberous sclerosis complex (TSC) syndrome can also develop RCC primarily mediated through mTOR signaling. However, the efficacy and duration of response of mTOR inhibition in patients with TSC-associated RCC is not well known. Herein, we describe a case of a patient with TSC2-associated metastatic RCC with mutations H1620R and Y1650C who has had an exceptional response to everolimus in the frontline setting and continues to derive benefit from mTOR inhibition 2 yr into therapy. Furthermore, the alteration H1620R in exon 37 resulting in a missense mutation is likely deleterious given our findings and previous analyses of the TSC2 gene. Further studies of somatic mutations in extended responders to mTOR inhibitors will help personalize therapy for these patients. It also emphasizes the value of targeted therapies based on genomic analyses.

Recent Advances and Challenges of mTOR Inhibitors Use in the Treatment of Patients with Tuberous Sclerosis Complex

Tuberous sclerosis complex (TSC) is a genetic condition characterized by the presence of benign, noninvasive, and tumor-like lesions called hamartomas that can affect multiple organ systems and are responsible for the clinical features of the disease. In the majority of cases, TSC results from mutations in the TSC1 and TSC2 genes, leading to the overactivation of the mammalian target of rapamycin (mTOR) signalling pathway, which controls several cell functions, including cell growth, proliferation, and survival. The establishment of a connection between TSC and mTOR led to the clinical use of drugs known as mTOR inhibitors (like rapamycin, also known as sirolimus and everolimus), which are becoming an increasingly interesting tool in the management of TSC-associated features, such as subependymal giant cell astrocytomas, renal angiomyolipomas, and also epilepsy. However, the intrinsic characteristics of these drugs and their systemic effects in such a heterogeneous condition pose many challenges in clinical practice, so that some questions remain unanswered. This article provides an overview of the pharmacological aspects of mTOR inhibitors about the clinical trials leading to their approval in TSC-related conditions and exposes current challenges and future directions associated with this promising therapeutic line.

Is mTOR Inhibitor Good Enough for Treatment All Tumors in TSC Patients?

Tuberous sclerosis complex (TSC) is an autosomal dominant and multi-system genetic disorder in humans. TSC affects around 25,000 to 40,000 individuals in the United States and about 1 to 2 million individuals worldwide, with an estimated prevalence of one in 6,000 newborns. TSC occurs in all races and ethnic groups, and in both genders. TSC is caused by defects or mutations in two genes, TSC1 and TSC2. Loss of TSC1/TSC2 leads to dysregulation of mTOR, resulting in aberrant cell differentiation and development, and abnormal enlargement of cells. TSC is characterized by the development of benign and/or malignant tumors in several organs including renal/liver angiomyolipomas, facial angiofibroma, lymphangiomyomatosis, cardiac rhabdomyomas, retinal astrocytic, renal cell carcinoma, and brain subependymal giant cell astrocytomas (SEGA). In addition, TSC disease causes disabling neurologic disorders, including epilepsy, mental retardation and autism. Particularly problematic are the development of renal angiomyolipomas, which tend to be larger, bilateral, multifocal and present at a younger age compared with sporadic forms. In addition, SEGA block the flow of fluid within the brain, causing a buildup of fluid and pressure that leads to blurred vision and seizures. In the current review, we describe the pathology of TSC disease in key organs and summarize the use of mTOR inhibitors to treat tumors in TSC patients.

Rapamycin and rapalogs for tuberous sclerosis complex

BACKGROUND

Previous studies have shown potential benefits of rapamycin or rapalogs for treating people with tuberous sclerosis complex. Although everolimus (a rapalog) is currently approved by the FDA (U.S. Food and Drug Administration) and the EMA (European Medicines Agency) for tuberous sclerosis complex-associated renal angiomyolipoma and subependymal giant cell astrocytoma, applications for other manifestations of tuberous sclerosis complex have not yet been established. A systematic review is necessary to establish the clinical value of rapamycin or rapalogs for various manifestations in tuberous sclerosis complex.

OBJECTIVES

To determine the effectiveness of rapamycin or rapalogs in people with tuberous sclerosis complex for decreasing tumour size and other manifestations and to assess the safety of rapamycin or rapalogs in relation to their adverse effects.

SEARCH METHODS

Relevant studies were identified by authors from the Cochrane Central Register of Controlled Trials (CENTRAL), Ovid MEDLINE, and clinicaltrials.gov. Relevant resources were also searched by the authors, such as conference proceedings and abstract books of conferences, from e.g. the Tuberous Sclerosis Complex International Research Conferences, other tuberous sclerosis complex-related conferences and the Human Genome Meeting. We did not restrict the searches by language as long as English translations were available for non-English reports.Date of the last searches: 14 March 2016.

SELECTION CRITERIA

Randomized or quasi-randomized studies of rapamycin or rapalogs in people with tuberous sclerosis complex.

DATA COLLECTION AND ANALYSIS

Data were independently extracted by two authors using standard acquisition forms. The data collection was verified by one author. The risk of bias of each study was independently assessed by two authors and verified by one author.

MAIN RESULTS

Three placebo-controlled studies with a total of 263 participants (age range 0.8 to 61 years old, 122 males and 141 females, with variable lengths of study duration) were included in the review. We found high-quality evidence except for response to skin lesions which was judged to be low quality due to the risk of attrition bias. Overall, there are 175 participants in the treatment arm (rapamycin or everolimus) and 88 in the placebo arm. Participants all had tuberous sclerosis complex as proven by consensus diagnostic criteria as a minimum. The quality in the description of the study methods was mixed, although we assessed most domains as having a low risk of bias. Blinding of treatment arms was successfully carried out in all of the studies. However, two studies did not report allocation concealment. Two of the included studies were funded by Novartis Pharmaceuticals.Two studies (235 participants) used oral (systemic) administration of everolimus (rapalog). These studies reported response to tumour size in terms of the number of individuals with a reduction in the total volume of tumours to 50% or more relative to baseline. Significantly more participants in the treatment arm (two studies, 162 participants, high quality evidence) achieved a 50% reduction in renal angiomyolipoma size, risk ratio 24.69 (95% confidence interval 3.51 to 173.41) (P = 0.001). For the sub-ependymal giant cell astrocytoma, our analysis of one study (117 participants, high quality evidence) showed significantly more participants in the treatment arm achieved a 50% reduction in tumour size, risk ratio 27.85 (95% confidence interval 1.74 to 444.82) (P = 0.02). The proportion of participants who showed a skin response from the two included studies analysed was significantly increased in the treatment arms, risk ratio 5.78 (95% confidence interval 2.30 to 14.52) (P = 0.0002) (two studies, 224 participants, high quality evidence). In one study (117 participants), the median change of seizure frequency was -2.9 in 24 hours (95% confidence interval -4.0 to -1.0) in the treatment group versus -4.1 in 24 hour (95% confidence interval -10.9 to 5.8) in the placebo group. In one study, one out of 79 participants in the treatment group versus three of 39 in placebo group had increased blood creatinine levels, while the median percentage change of forced expiratory volume at one second in the treatment arm was -1% compared to -4% in the placebo arm. In one study (117 participants, high quality evidence), we found that those participants who received treatment had a similar risk of experiencing adverse events compared to those who did not, risk ratio 1.07 (95% confidence interval 0.96 - 1.20) (P = 0.24). However, as seen from two studies (235 participants, high quality evidence), the treatment itself led to significantly more adverse events resulting in withdrawal, interruption of treatment, or reduction in dose level, risk ratio 3.14 (95% confidence interval 1.82 to 5.42) (P < 0.0001).One study (28 participants) used topical (skin) administration of rapamycin. This study reported response to skin lesions in terms of participants' perception towards their skin appearance following the treatment. There was a tendency of an improvement in the participants' perception of their skin appearance, although not significant, risk ratio 1.81 (95% confidence interval 0.80 to 4.06, low quality evidence) (P = 0.15). This study reported that there were no serious adverse events related to the study product and there was no detectable systemic absorption of the rapamycin during the study period.

AUTHORS' CONCLUSIONS

We found evidence that oral everolimus significantly increased the proportion of people who achieved a 50% reduction in the size of sub-ependymal giant cell astrocytoma and renal angiomyolipoma. Although we were unable to ascertain the relationship between the reported adverse events and the treatment, participants who received treatment had a similar risk of experiencing adverse events as compared to those who did not receive treatment. Nevertheless, the treatment itself significantly increased the risk of having dose reduction, interruption or withdrawal. This supports ongoing clinical applications of oral everolimus for renal angiomyolipoma and subependymal giant cell astrocytoma. Although oral everolimus showed beneficial effect on skin lesions, topical rapamycin only showed a non-significant tendency of improvement. Efficacy on skin lesions should be further established in future research. The beneficial effects of rapamycin or rapalogs on tuberous sclerosis complex should be further studied on other manifestations of the condition.

Rapamycin and its analogues (rapalogs) for Tuberous Sclerosis Complex-associated tumors: a systematic review on non-randomized studies using meta-analysis

Background

Rapamycin has gained significant attention for its potential activity in reducing the size of TSC-associated tumors, thus providing alternative to surgery. This study aimed at determining the efficacy of rapamycin and rapalogs for reducing the size of TSC-associated solid tumors in patients with Tuberous Sclerosis Complex (TSC).

Methods

Our data sources included electronic searches of the PubMed. We included into our meta-analysis any type of non-randomized study that reported the use of rapamycin and rapalogs for reducing the size of TSC-associated solid tumors in patients with TSC. Data was entered into Cochrane Review Manager Version 5.3 and analyzed.

Results

Four case reports and 4 clinical trials were included. Five patients from the case reports (all with SEGA) and 91 patients from the clinical trials (41 with SEGA, 63 with kidney angiomyolipoma and 5 with liver angiomyolipoma) were included into the analysis. Volume and diameter of SEGAs were significantly reduced by mean difference of 1.23 cc (95 % CI −2.32 to −0.13; p = 0.03) and 7.91 mm (95 % CI −11.82 to −4.01; p < 0.0001), respectively. Volume and mean of sum of longest diameter of kidney angiomyolipomas were significantly reduced by mean difference of 39.5 cc (95 % CI −48.85 to −30.15; p <0.00001) and 69.03 mm (95 % CI −158.05 to 12.65; p = 0.008), respectively. In liver angiomyolipomas, however, reduction in tumor size was not evident. Sum of longest diameter of liver angiomyolipomas in 4 patients were enlarged by 2.7 mm (95 % CI 28.42 to −23.02) by the end of treatment, though not significant (p = 0.84).

Conclusions

Rapamycin and rapalogs showed efficacy towards reducing the size of SEGA and kidney angiomyolipoma but not liver angiomyolipomas. This finding is strengthening the conclusion of our Cochrane systematic review on the randomized trials.

Advances in therapy for pediatric sarcomas

Pediatric sarcomas are relatively rare malignancies individually. As a group they are typically approached with combination chemotherapies in addition to local control. Fortunately, these malignancies have been approached through careful clinical trial collaboration to define risk groups and appropriately deliver local control measures and systemic therapies. Although local disease is typically approached with curative intent, therapy typically lasts over 6 months and has significant associated morbidities. It is more difficult to cure metastatic disease or induce sustained remissions. In this article, we discuss recent advances in the understanding of the disease process and highlight recent and future cooperative group trials in osteosarcoma, Ewing sarcoma, rhabdomyosarcoma, nonrhabdomyosarcoma soft tissue sarcomas, and desmoid tumor as well as discuss promising therapeutic approaches such as epigenetics and immunotherapy.

Efficacy and safety of a mammalian target of rapamycin inhibitor in pediatric patients with tuberous sclerosis complex: A systematic review and meta-analysis

Inhibitors of mammalian target of rapamycin (mTOR) are increasingly used as therapy for pediatric patients with tuberous sclerosis complex (TSC). The uncertainty over the efficacy and safety of mTOR inhibitor therapy for the treatment of pediatric patients with TSC emphasizes the necessity for a synthesis of existing evidence. The aim of this study was to assess the efficacy and safety of mTOR inhibitor therapy for the treatment of pediatric patients with TSC. The PubMed, EmBase and Cochrane Library electronic databases were searched, and studies of mTOR inhibitor therapy and non-mTOR inhibitor therapy in pediatric patients with TSC (<18 years old) were selected. Eleven studies met the inclusion criteria. There was evidence of a significantly increased response rate in pediatric patients with TSC treated with mTOR inhibitor therapy compared with those treated with non-mTOR inhibitor therapy (odds ratio, 24.71; 95% confidence interval, 7.46–81.72; P<0.001). The majority of studies reported few adverse events. There was an increased incidence of mouth ulceration, stomatitis, convulsion and pyrexia in pediatric patients with TSC treated with mTOR inhibitor therapy. In conclusion, mTOR inhibitor therapy is an efficacious and safe treatment for pediatric patients with TSC.

The use of everolimus to target carcinogenic pathways in a patient with renal cell carcinoma and tuberous sclerosis complex: a case report

INTRODUCTION

An increased understanding of the genetic pathways involved in renal cell carcinoma has resulted in the development of various drugs that target relevant signaling cascades for the specific treatment of this disease. However, no validated predictive markers have been identified to guide the decision whether patients should receive vascular endothelial growth factor-targeted therapy or mammalian target of rapamycin-targeted therapy. We present what is, to the best of our knowledge, the first case of renal cell carcinoma in a patient with tuberous sclerosis complex who was successfully treated with everolimus.

CASE PRESENTATION

The patient was a 49-year-old Korean woman with tuberous sclerosis complex and recurrent renal cell carcinoma. The patient was treated with the tyrosine kinase inhibitor sunitinib followed by the mammalian target of rapamycin inhibitor everolimus. This treatment resulted in a prolonged response and significant clinical benefit. Notably, everolimus ameliorated the symptoms related not only to renal cell carcinoma but also to tuberous sclerosis complex.

CONCLUSION

This case provides a rationale for the use of everolimus as first-line treatment for this specific patient population in order to target the correct pathway involved in carcinogenesis.

Therapeutic targeting of cancers with loss of PTEN function

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) is one of the most frequently disrupted tumor suppressors in cancer. The lipid phosphatase activity of PTEN antagonizes the phosphatidylinositol 3-kinase (PI3K)/AKT/mTOR pathway to repress tumor cell growth and survival. In the nucleus, PTEN promotes chromosome stability and DNA repair. Consequently, loss of PTEN function increases genomic instability. PTEN deficiency is caused by inherited germline mutations, somatic mutations, epigenetic and transcriptional silencing, post-translational modifications, and protein-protein interactions. Given the high frequency of PTEN deficiency across cancer subtypes, therapeutic approaches that exploit PTEN loss-of-function could provide effective treatment strategies. Herein, we discuss therapeutic strategies aimed at cancers with loss of PTEN function, and the challenges involved in treating patients afflicted with such cancers. We review preclinical and clinical findings, and highlight novel strategies under development to target PTENdeficient cancers.

Dissecting the PI3K Signaling Axis in Pediatric Solid Tumors: Novel Targets for Clinical Integration

Children with solid tumors represent a unique population. Recent improvements in pediatric solid tumor survival rates have been confined to low- and moderate-risk cancers, whereas minimal to no notable improvement in survival have been observed in high-risk and advanced-stage childhood tumors. Treatments for patients with advanced disease are rarely curative, and responses to therapy are often followed by relapse, which highlights the large unmet need for novel therapies. Recent advances in cancer treatment have focused on personalized therapy, whereby patients are treated with agents that best target the molecular drivers of their disease. Thus, a better understanding of the pathways that drive cancer or drug resistance is of critical importance. One such example is the phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway, which is activated in many solid cancer patients and represents a target for therapy. PI3K/Akt/mTOR pathway activation has also been observed in tumors resistant to agents targeting upstream receptor tyrosine kinases (RTKs). Agents that target this pathway have the potential to shut down survival pathways, and are being explored both in the setting of pathway-activating mutations and for their ability to restore sensitivity to upstream signaling targeted agents. Here, we examine the role of the PI3K/Akt/mTOR pathway in pediatric solid tumors, review the novel agents being explored to target this pathway, and explore the potential role of the inhibition of this pathway in the clinical development of these agents in children.

mTOR Inhibitors in Tuberous Sclerosis Complex

Tuberous sclerosis complex (TSC) is a genetic multiple organ system disorder that is characterized by the development of tumor-like lesions (hamartomas) and neurodevelopmental disorders. Mutations in the TSC1 and TSC2 tumor suppressor genes occur in the majority of patients with TSC, resulting in hyperactivation of the mammalian target of rapamycin (mTOR) signaling pathway and subsequent abnormalities in numerous cell processes. As a result, mTOR inhibitors such as sirolimus and everolimus have the potential to provide targeted therapy for patients with TSC. Everolimus is the first mTOR inhibitor approved as a treatment option in the USA and in Europe for patients with subependymal giant-cell astrocytomas (SEGAs) associated with TSC. The clinical evidence to date supports the use of mTOR inhibitors in a variety of TSC-associated disease manifestations, including SEGAs, renal angiomyolipoma, skin manifestations, and epilepsy. Furthermore, ongoing clinical trials evaluating mTOR inhibitors in TSC are underway, and the results of these studies are expected to provide further evidence that will firmly establish their role in this setting. This article will discuss the role of the mTOR pathway in TSC and review the pharmacokinetics, pharmacodynamics, clinical efficacy, and tolerability of mTOR inhibitors, along with their current place in clinical practice.