Non-melanoma skin cancer is reduced after switch of immunosuppression to mTOR-inhibitors in organ transplant recipients

[The Cutaneous Squamous Cell Carcinoma - An Update]

BACKGROUND

The cutaneous squamous cell carcinoma (CSCC) is the second most common nonmelanoma skin cancer with an increasing incidence rate. Patients presenting with high-risk lesions associated with locally advanced or metastatic CSCC face high rates of recurrence and mortality.

METHODS

Selective literature review based on PubMed and consideration of current guidelines "Aktinische Keratosen und Plattenepithelkarzinom der Haut" and "Prävention von Hautkrebs".

FINDINGS

Complete surgical excision with histopathological control of excision margins is the gold standard in the treatment of primary CSCC. Radiotherapy can be used as an alternative treatment of inoperable CSCCs. In 2019, the PD1-antibody cemiplimab, has been approved for the treatment of locally advanced and metastatic CSCC by the European Medicines Agency. After 3 years of follow up, Cemiplimab shows overall response rates of 46 %, the median overall survival and median response rate had not been reached yet. Additional immunotherapeutics, combinations with other agents and oncolytic viruses are all potentially worth study to try, so clinical trial data will be forthcoming over the next few years to guide optimal use of these agents.

CONCLUSION

Multidisciplinary board decisions are mandatory for all patients with advanced disease who require more than surgery. Further development of existing therapeutic concepts, identification of new combination therapies and the development of new immunotherapeutics will be the key challenge over the next few years.

Topical treatment of actinic keratoses in organ transplant recipients: a feasibility study for SPOT (Squamous cell carcinoma Prevention in Organ transplant recipients using Topical treatments)

BACKGROUND

The risk of cutaneous squamous cell carcinoma (cSCC) is significantly increased in organ transplant recipients (OTRs). Clearance of actinic keratoses (AKs) is generally regarded as a surrogate biomarker for cSCC prevention. OTR-cSCC chemoprevention with topical AK treatments has not been investigated in randomized controlled trials (RCTs), although there is evidence that 5% 5-fluorouracil (5-FU) may be chemoprotective in immunocompetent patients.

OBJECTIVES

To assess the feasibility, activity and evaluation outcomes relevant to the design of a future phase III RCT of topical cSCC chemoprevention in OTRs.

METHODS

OTRs with 10 or more AKs in predefined areas were randomized 1 : 1 : 1 to topical 5-FU, 5% imiquimod (IMIQ) or sunscreen (sun-protective factor 30+) in a phase II, open-label RCT over 15 months. Feasibility outcomes included proportions of eligible OTRs randomized, completing treatment and willing to be re-treated. AK activity [AK clearance, new AK development, patient-centred outcomes (toxicity, health-related quality of life, HRQoL)] and evaluation methodology (clinical vs. photographic) were assessed.

RESULTS

Forty OTRs with 903 AKs were randomized. All feasibility outcomes were met (56% of eligible OTRs were randomized; 89% completed treatment; 81% were willing to be re-treated). AK activity analyses found 5-FU and IMIQ were superior to sunscreen for AK clearance and prevention of new AKs. 5-FU was more effective than IMIQ in AK clearance and prevention in exploratory analyses. Although toxicity was greater with 5-FU, HRQoL outcomes were similar.

CONCLUSIONS

Trials of topical AK treatments in OTRs for cSCC chemoprevention are feasible and AK activity results support further investigation of 5-FU-based treatments in future phase III trials. What is already known about this topic? Cutaneous squamous cell carcinoma (cSCC) is significantly more common in immunocompromised individuals including organ transplant recipients (OTRs) compared with immunocompetent populations. cSCC chemoprevention activity of sunscreen and 5-fluorouracil-based (5-FU) actinic keratosis (AK) treatments has been demonstrated in randomized controlled trials (RCTs) in immunocompetent populations but not in OTRs. AKs are cSCC precursors and their clearance and prevention are generally regarded as surrogate endpoint biomarkers for potential cSCC chemoprevention activity. What does this study add? SPOT (SCC Prevention in OTRs using Topical treatments) has confirmed that RCTs of OTR-cSCC chemoprevention with topical AK treatments are feasible. It also suggests that topical 5-FU may be superior to 5% imiquimod and sunscreen in AK clearance and prevention. Together with recent evidence from several RCTs in the general population, these data provide a compelling rationale for further studies of intervention with 5-FU-based topical chemoprevention approaches in OTR-cSCC prevention.

Mammalian Target of Rapamycin Inhibitors for prolonged secondary prevention of non-melanoma skin cancer in solid organ transplant recipients

BACKGROUND

Immunosuppressive agents are essential for graft survival in solid-organ transplant recipients (SOTRs), but they have substantial durable side effects, including a higher incidence of aggressive non-melanoma skin cancers (NMSCs). Hitherto, only one class of immunosuppressants, mammalian target of rapamycin inhibitors (mTORi), may inhibit skin tumor formation, however their durable effectiveness is controversial.

OBJECTIVE

To evaluate the sustained effectiveness of mTORi in reducing NMSCs' incidence in SOTRs.

METHODS

A retrospective study was conducted in a specialized dermatology clinic for SOTRs of a tertiary university-affiliated medical center. SOTRs with a history of at least one histologically proven NMSC, were followed for 6 years: 3 years after transplantation, before initiation of mTORi, and 3 years under mTORi treatment.

RESULTS

The cohort consisted of 44 SOTRs. Treatment with mTORi was initiated on average 6.27 (3.34-6.34) years following transplantation. In the 3 years before mTORi treatment initiation, the mean number of new NMSCs per patient was 2.11 (1-14). This value decreased to 1.2 (0-19) in the 3 years under mTORi treatment (P=0.0007). Analysis by NMSC type yielded a significant decrease in both SCCs and BCCs.

CONCLUSION

This study found that mTORi are effective for prolonged secondary prevention of NMSCs in SOTRs. This article is protected by copyright. All rights reserved.

Das kutane Plattenepithelkarzinom – ein Update

Hintergrund Das kutane Plattenepithelkarzinom (PEK) ist nach dem Basalzellkarzinom der zweithäufigste bösartige Hauttumor. In Deutschland wurden 2014 über 50.000 PEK-Neuerkrankungen dokumentiert. Mit Zunahme der durchschnittlichen Lebenserwartung und Komorbiditäten treten mittlerweile auch gehäuft lokal fortgeschrittene Tumore mit Metastasierung auf.

Methode Selektive Literaturrecherche in PubMed und unter Berücksichtigung der deutschen S3-Leitlinien „Aktinische Keratosen und Plattenepithelkarzinom der Haut“ und „Prävention von Hautkrebs“.

Ergebnisse Beim PEK ist der Goldstandard die vollständige Exzision des Primärtumors mittels histopathologischer Kontrolle der Schnittränder. Eine Radiotherapie kann eingesetzt werden, wenn eine vollständige Exzision nicht erreicht werden kann bzw. Inoperabilität besteht. Im Falle eines metastasierten (mPEK) oder lokal fortgeschrittenen (laPEK) PEK, welches nicht kurativ operiert oder bestrahlt werden kann, werden systemische medikamentöse Therapien eingesetzt. Mit der Zulassung des PD1-Antikörpers Cemiplimab steht seit 2019 in der EU eine neue systemische Therapie zur Behandlung des fortgeschrittenen PEK zur Verfügung. Nach bis zu 3 Jahren Follow-up sprechen noch 46% der Patienten mit mPEK und laPEK auf Cemiplimab an, der Medianwert für das Gesamtüberleben und die Ansprechdauer ist in beiden Gruppe noch nicht erreicht. Weitere Antikörper gegen PD1 oder PDL1, Kombinationstherapien sowie die Immuntherapie mit onkolytischen Viren ermöglichen zahlreiche Therapieoptionen und sind aktuell Gegenstand der Forschung.

Schlussfolgerung Mit der Zunahme von fortgeschrittenen Stadien des PEK nimmt die Wichtigkeit des interdisziplinären Tumorboards für den Therapieentscheid immer mehr zu. Die Weiterentwicklung bestehender therapeutischer Konzepte, die Identifikation von gut wirksamen Kombinationstherapien sowie die Entwicklung weiterer verträglicher zielgerichteter Systemtherapien ist eine entscheidende dermatoonkologische Herausforderung der nächsten Jahre.

Update aktinische Keratosen – Neuigkeiten und Relevanz für den Alltag

Ziel der Arbeit Die im März 2020 zuletzt überarbeitete Leitlinie „Aktinische Keratosen und Plattenepithelkarzinome der Haut“ hat aufgrund der Zunahme der klinischen Studien zum Thema aktinische Keratosen den höchsten Grad für Methodik (S3) erreicht, da diese nicht nur konsensbasiert sondern auch evidenzbasiert verfasst wurde. Diesen Entwicklungen gerecht zu werden und den klinisch relevanten Teil des aktuellen Stands des Wissens zu vermitteln, ist Ziel dieses Artikels.

Methodik Anhand der aktuellen epidemiologischen Lage wird der dramatisch wachsende Bedarf für das bessere Verständnis der Ätiologie aktinischer Keratosen deutlich. Ebenso gilt es, Patienten mit aktinischen Keratosen und therapiebedürftigen Ko-Morbiditäten vor einem therapiebedingten, erhöhten Risiko für die Entwicklung weiterer aktinischer Keratosen oder Plattenepithelkarzinomen zu bewahren. Die Möglichkeit der Spontanremission aktinischer Keratosen sollte ebenso wenig vernachlässigt werden wie eine mögliche Progredienz in ein Plattenepithelkarzinom. Die kontroverse Diskussion der fortwährend postulierten, sequenziellen Abfolge der histologischen Grade aktinischer Keratosen zum Plattenepithelkarzinom beinhaltet klinische und histologische Fallstricke. Diese sollten bei der Therapieentscheidung ebenso bedacht werden wie die Wünsche und Erwartungen der Patienten an ein Therapieregime. Eine bleibende Schwierigkeit ist die fehlende Standardisierung erhobener Daten zu den zahlreichen zur Verfügung stehenden Therapieoptionen. Das Potenzial dieses Forschungsgebietes für neue Therapiealternativen und präventive Maßnahmen lässt nach wie vor auf weitere, interessante Entwicklungen hoffen.

Ergebnisse Der gut etablierte kausale Zusammenhang zwischen kumulativer UV-Strahlung in der Entwicklung von Plattenepithelkarzinomen und aktinischer Keratosen hat zur Anerkennung berufsbedingter UV-Exposition als Berufserkrankung geführt, die auch die Anerkennung multipler aktinischer Keratosen als Berufserkrankung beinhaltet. Das therapeutische Handeln sollte durch die Gesamtanzahl der aktinischen Keratosen, das Ausmaß der betroffenen Fläche, die Dynamik des Krankheitsgeschehens und den Wunsch des Patienten bestimmt werden. Ein besonderes Augenmerk sollte auf den Patienten liegen, denen die Krankheitseinsicht fehlt oder die nur wenig motiviert zur Therapie sind. Es könnte der Schlüssel zur Verbesserung der Therapieadhärenz und Akzeptanz sein, diese Patienten zu erkennen und ihre Bedürfnisse in das Arzt-Patienten-Gespräch zu integrieren. Die Differenzierung zwischen lokalisierten aktinischen Keratosen und einer Feldkanzerisierung stellt ein wichtiges Entscheidungskriterium für die Wahl der empfohlenen Therapie dar. Die Rücknahme der Zulassung von Ingenolmebutat in der EU durch die EMA im Jahr 2020 hat das Spektrum der lokaltherapeutischen Optionen eingeschränkt. Der periinterventionelle Schmerz ist nach wie vor der limitierende Faktor für die konventionelle photodynamische Therapie, jedoch schreitet die Entwicklung für schmerzärmere Varianten weiter voran. Es ist zu erwarten, dass sich in den kommenden Jahren durch eine bessere Evidenzlage für weitere systemische oder lokaltherapeutische Optionen neue Behandlungsstrategien ergeben werden. Besonders im Fokus wird sicherlich nach wie vor die Präventionsforschung stehen, die v. a. den Erhalt einer erzielten Remission beinhaltet.

Schlussfolgerung Die aktuellen Forschungsergebnisse und -bestrebungen zur Thematik der aktinischen Keratosen sind aufgrund des zukünftig gesteigerten Bedarfes zum einen notwendig und zum anderen sehr ermutigend. Das Ende des therapeutischen Horizonts ist gegenwärtig noch nicht erreicht.

Skin cancers in Italian lung transplant recipients: Incidence and risk factors analysis

Only a few studies reported the incidence and risk factors of skin cancers in lung transplant recipients. The aim of this study was to determine the cumulative incidence of skin cancers in a cohort of patients undergoing lung transplantation and to define predictors of their development. About 247 consecutive patients receiving lung transplantation at the Thoracic Surgery Unit of University Hospital of Padova between May 1995 and October 2016 were studied. Cumulative incidence of skin cancers was estimated considering death as a competing event. The effect of potential predictors was evaluated with univariate and multivariable Cox models for competing risks. About 37 (15.0%) patients developed skin tumors. The cumulative incidence of any skin cancer was 14.2% at 5 years, 21.4% at 10 years, and 24.3% at 15 years posttransplantation. Age at transplantation, male gender, phototype II, and voriconazole use were independent risk factors for development of squamous cell carcinoma. Only male gender and phototype II were independent risk factors for development of basal cell carcinoma. Since lung transplant recipients have a greater risk of developing skin cancers, the management of these patients needs a multidisciplinary approach, in which dermatologists and transplant physicians have a primary role.

Actinic Keratosis and Cutaneous Squamous Cell Carcinoma

BACKGROUND

Cutaneous squamous cell carcinoma (cSCC) and its precursors, actinic keratoses (AK), are common. Physicians of multiple specialties are confronted with their treatment.

METHODS

This review is based on publications retrieved by a selective search in PubMed, as well as on the German guidelines on AK and cSCC, skin cancer prevention, and surgery with histologic guidance.

RESULTS

Local treatments for AK include lesional cryotherapy, curettage, and laser ablation as well as field-directed treatments with topical agents, e.g., diclofenac plus hyaluronic acid, imiquimod, 5-fluorouracil, ingenol mebutate, and photodynamic therapy. These treatments can be administered in various sequences or combinations, depending on individual factors and the stage of the disease. The gold standard of treatment for cSCC is histologically confirmed complete resection; radiotherapy is an alternative. Locally uncontrollable or metastatic disease is treated with systemic drugs. The use of various chemotherapeutic agents, EGFR-directed therapies, and the PD-I inhibitor cemiplimab, either singly or in combination, has been described in uncontrolled trials and case series. Cemiplimab has a reported response rate of 47% and was recently approved for the treatment of advanced cSCC.

CONCLUSION

There are many options for the treatment of AK and cSCC that must be considered in the interdisciplinary care of these entities.

Risk Factors for Developing Nonmelanoma Skin Cancer after Lung Transplantation

Background

Nonmelanoma skin cancer (NSMC) is the most common malignancy after organ transplantation. Lung transplant recipients (LTRs) are particularly prone to develop NMSC as compared to renal or hepatic transplant recipients due to higher dosages of immunosuppression needed. Everolimus, an immunosuppressant used in organ transplant recipients, is thought to inherit a lower risk for NMSC than calcineurin inhibitors, especially in renal transplant recipients. It is currently unknown whether this also applies to LTRs.

Objectives

To determine risk factors for NMSC and precancerous lesions after lung transplantation (LTx) and to characterize the effect of everolimus-based regimens regarding this risk.

Materials and Methods

90 LTRs and former participants of the interventional trial “Immunosuppressive Therapy with Everolimus after Lung Transplantation”, who were randomized to receive either an everolimus- or mycophenolate mofetil- (MMF-) based regimen, were enrolled and screened in this retrospective, single-center cohort study.

Results

After a median follow-up of 101 months, we observed a prevalence of 38% for NMSC or precancerous lesions. 33% of the patients continuously receiving everolimus from LTx to dermatologic examination compared to 39% of all other patients, predominantly receiving an MMF-based regimen, were diagnosed with at least one NMSC or precancerous lesion (P=.66). Independent risk factors for NMSC or precancerous lesions after LTx were male sex and duration of voriconazole therapy.

Conclusion

NMSC or precancerous lesions were very common after LTx, and risk factors were similar to previous reports on LTRs. Everolimus did not decrease this risk under the given circumstances of this study. Patients should be counseled regarding their risk, perform vigorous sunscreen, and undergo regular dermatological controls, regardless of their immunosuppressive regimen.

Polygenic risk score as a determinant of risk of non-melanoma skin cancer in a European-descent renal transplant cohort

Renal transplant recipients have an increased risk of non-melanoma skin cancer (NMSC) compared to in the general population. Here, we show polygenic risk scores (PRS) calculated from genome-wide association studies (GWAS) of NMSC in a general, nontransplant setting, can predict risk of, and time to posttransplant skin cancer. Genetic variants, reaching predefined P-value thresholds were chosen from published squamous cell carcinoma (SCC) and basal cell carcinoma (BCC) nontransplant GWAS. Using these GWAS, BCC and SCC PRS were calculated for each sample across three European ancestry renal transplant cohorts (n = 889) and tested as predictors of case:control status and time to NMSC posttransplant. BCC PRS calculated at P-value threshold 1 × 10-5 was the most significant predictor of case:control status of NMSC posttransplant (OR = 1.61; adjusted P = .0022; AUC [full model adjusted for clinical predictors and PRS] = 0.81). SCC PRS at P-value threshold 1 × 10-5 was the most significant predictor of time to posttransplant NMSC (adjusted P = 9.39 × 10-7 ; HR = 1.41, concordance [full model] = 0.74). PRS of nontransplant NMSC is predictive of case:control status and time to NMSC posttransplant. These results are relevant to how genomics can risk stratify patients to help develop personalized treatment regimens.

From rapalogs to anti-aging formula

Inhibitors of mTOR, including clinically available rapalogs such as rapamycin (Sirolimus) and Everolimus, are gerosuppressants, which suppress cellular senescence. Rapamycin slows aging and extends life span in a variety of species from worm to mammals. Rapalogs can prevent age-related diseases, including cancer, atherosclerosis, obesity, neurodegeneration and retinopathy and potentially rejuvenate stem cells, immunity and metabolism. Here, I further suggest how rapamycin can be combined with metformin, inhibitors of angiotensin II signaling (Losartan, Lisinopril), statins (simvastatin, atorvastatin), propranolol, aspirin and a PDE5 inhibitor. Rational combinations of these drugs with physical exercise and an anti-aging diet (Koschei formula) can maximize their anti-aging effects and decrease side effects.

[Cutaneous squamous cell carcinoma]

Squamous cell carcinoma (SCC) of the skin accounts for 20 % of non-melanoma skin cancer and is one of the most frequent types of cancer in Caucasian populations. Diagnosis is based on the clinical features and should be histopathologically confirmed to adequately address the prognosis and treatment. Complete surgical excision with histopathological control of excision margins is the gold standard in the treatment of primary SCC. Sentinel lymph node biopsies (SLNB) can be considered in SCC with a tumor thickness of >6 mm but there is currently no evidence concerning prognostic and therapeutic effects. Radiotherapy can be discussed as an alternative to surgery for inoperable tumors or as adjuvant therapy for a high risk of recurrence. In SCC with distant metastases various chemotherapeutic agents are used; however, there is no standard regimen. The epidermal growth factor receptor (EGFR) inhibitors and immune checkpoint blockers can be discussed as treatment options, preferentially in clinical trials. There is no standard follow-up schedule for patients with SCC. A risk-adapted follow-up is recommended based on the risk of metastatic spread or development of new lesions primarily by dermatological control and supplemented by ultrasound investigations in high risk patients.

While reinforcing cell cycle arrest, rapamycin and Torins suppress senescence in UVA-irradiated fibroblasts

Sunlight predisposes to skin cancer and melanomas. Ultraviolet A (UVA), a long wave component of sunlight, can reach dermal fibroblasts. Here we studied UVA-induced senescence in human fibroblasts in vitro. It is known that senescence occurs, when cell cycle is arrested, but mTOR is still active, thus converting arrest to senescence (geroconversion). We showed that, while arresting cell cycle, UVA did not inhibit mTOR, enabling geroconversion. In UVA-treated cells, mTOR remained fully active. Rapamycin and Torins 1/ 2 prevented UVA-induced senescent phenotype, although they further re-enforced cell cycle arrest. Given that senescent stromal fibroblasts support tumorigenesis, we envision that mTOR inhibitors may potentially be used to prevent sunlight-caused tumors as well as skin photo-aging.

Individualized Immunosuppressive Protocol of Liver Transplant Recipient Should be Made Based on Splenic Function Status

BACKGROUND

Lymphocyte subsets play important roles in rejection in liver transplant recipients, and the effect of splenic function on these roles remains unknown. The aim of this study was to explore the feasibility to adjust immunosuppressive agents based on splenic function status through detecting the lymphocyte subsets in liver transplantBeijing recipients.

METHODS

The lymphocyte subsets of 49 liver transplant recipients were assessed in the 309th Hospital of Chinese People's Liberation Army between June 2014 and August 2015. The patients were divided into splenectomy group (n = 9), normal splenic function group (n = 24), and hypersplenism group (n = 16). The percentages and counts of CD4+ T, CD8+ T, natural killer (NK) cell, B-cell, regulatory B-cell (Breg), and regulatory T-cell (Treg) were detected by flow cytometer. In addition, the immunosuppressive agents, histories of rejection and infection, and postoperative time of the patients were compared among the three groups.

RESULTS

There was no significant difference of clinical characteristics among the three groups. The percentage of CD19+CD24+CD38+ Breg was significantly higher in hypersplenism group than normal splenic function group and splenectomy group (3.29 ± 0.97% vs. 2.12 ± 1.08% and 1.90 ± 0.99%, P = 0.001). The same result was found in CD4+CD25+FoxP3+ Treg percentage (0.97 ± 0.39% vs. 0.54 ± 0.31% and 0.56 ± 0.28%, P = 0.001). The counts of CD8+ T-cell, CD4+ T-cell, and NK cell were significantly lower in hypersplenism group than normal splenic function group (254.25 ± 149.08 vs. 476.96 ± 225.52, P= 0.002; 301.69 ± 154.39 vs. 532.50 ± 194.42, P= 0.000; and 88.56 ± 63.15 vs. 188.33 ± 134.51, P = 0.048). Moreover, the counts of CD4+ T-cell and NK cell were significantly lower in hypersplenism group than splenectomy group (301.69 ± 154.39 vs. 491.89 ± 132.31, P= 0.033; and 88.56 ± 63.15 vs. 226.00 ± 168.85, P = 0.032).

CONCLUSION

Splenic function status might affect the immunity of liver transplant recipients, that should be considered when we make immunosuppressive protocols.

Everolimus and Malignancy after Solid Organ Transplantation: A Clinical Update

Malignancy after solid organ transplantation remains a major cause of posttransplant mortality. The mammalian target of rapamycin (mTOR) inhibitor class of immunosuppressants exerts various antioncogenic effects, and the mTOR inhibitor everolimus is licensed for the treatment of several solid cancers. In kidney transplantation, evidence from registry studies indicates a lower rate of de novo malignancy under mTOR inhibition, with some potentially supportive data from randomized trials of everolimus. Case reports and small single-center series have suggested that switch to everolimus may be beneficial following diagnosis of posttransplant malignancy, particularly for Kaposi's sarcoma and nonmelanoma skin cancer, but prospective studies are lacking. A systematic review has shown mTOR inhibition to be associated with a significantly lower rate of hepatocellular carcinoma (HCC) recurrence versus standard calcineurin inhibitor therapy. One meta-analysis has concluded that patients with nontransplant HCC experience a low but significant survival benefit under everolimus monotherapy, so far unconfirmed in a transplant population. Data are limited in heart transplantation, although observational data and case reports have indicated that introduction of everolimus is helpful in reducing the recurrence of skin cancers. Overall, it can be concluded that, in certain settings, everolimus appears a promising option to lessen the toll of posttransplant malignancy.

Skin cancer in solid organ transplant recipients: are mTOR inhibitors a game changer?

While immunosuppressive agents are necessary to prevent the rejection of transplanted organs, and are a great medical success story for protecting against early allograft loss, graft and patient survival over the long term are diminished by side effects from these same drugs. One striking long-term side effect is a high rate of skin cancer development. The skin cancers that develop in transplant recipients tend to be numerous, as well as particularly aggressive, and are therefore a major contributor to morbidity and mortality in transplant recipients. An apparent reason for the high incidence of skin cancer likely relates to suppression of immune surveillance mechanisms, but other more direct effects of certain immunosuppressive drugs are also bound to contribute to cancers of UV-exposed skin. However, over the past few years, evidence has emerged to suggest that one class of immunosuppressants, mammalian target of rapamycin (mTOR) inhibitors, could potentially inhibit skin tumour formation through a number of mechanisms that are still being studied intensively today. Therefore, in light of the high skin cancer incidence in transplant recipients, it follows that clinical trials have been conducted to determine if mTOR inhibitors can significantly reduce these post-transplant skin malignancies. Here, the problem of post-transplant skin cancer will be briefly reviewed, along with the possible mechanisms contributing to this problem, followed by an overview of the relevant clinical trial results using mTOR inhibitors.