“The Adrenal Gland: Central Relay in Health and Disease - Current Challenges and Perspectives 2018” – Cushing’s Disease

Abstract

Background Despite advances in diagnostic and therapeutic approach, Cushing’s disease (CD) presents a challenging situation for the treating physician.

Aims To elucidate current challenges, present strengths and pitfalls of existing diagnostic tests, enlighten the need for new diagnostic approaches, appraise the effects of surgery and available pharmacological agents and identify future perspectives regarding CD.

Materials and methods Systematic search to PubMed and Medline databases for publications mainly over the last five years.

Results Mutations in the ubiquitin specific peptidase 8 gene have been recently identified in functional sporadic corticotroph adenomas causing CD. Since the prevalence of obesity and metabolic syndrome is rapidly increasing, new diagnostic tests are necessary to differentiate these conditions. Next to the traditional tests, a cutoff of preoperative ACTH/cortisol ratio, an ultrasensitive late night salivary cortisol assay and the desmopressin test have been suggested as valid tools for the diagnosis and differential diagnosis of CD. Transsphenoidal surgery with variable remission and recurrence rates presents the treatment of choice for CD. Medical therapy consists of adrenal-targeted drugs e. g. ketoconazole, metyrapone, etomidate and mitotane and pituitary-targeted drugs e. g. pasireotide, cabergoline and retinoic acid.

Conclusions CD is associated to a significant clinical burden, since numerous comorbidities persist after long-term biochemical control. These chronically ill patients show an increased mortality despite disease remission. Clinicians should treat comorbidities aggressively and seek for appropriate consultations. Structured consultation hours and expert excellence networks are needed in order to allow optimal, individualized care for affected patients, reverse increased morbidity and mortality and identify tumor recurrence early.

Key words

Cushing’s disease - signs and symptoms - diagnostic tests - transsphenoidal surgery - medical therapy - comorbidities

Abbreviations

ACTH: adrenocorticotropin

BA: bilateral adrenalectomy

BIPSS: bilateral inferior petrosal sinus sampling

BMI: body mass index

CD: Cushing’s disease

CRT: conventional photon beam radiotherapy

CS: Cushing’s syndrome

CYP11β: 11-beta-hydroxylase

CYP17A1: 17-alfa-hydroxylase

ECLIA: automated electrochemiluminescence immunoassay

ERCUSYN: European Registry on Cushing’s syndrome

GK: GammaKnife

hCRH: human corticotropin-releasing hormone

HDDST: high-dose dexamethasone suppression test

HPA: hypothalamus-pituitary-adrenal

HRQoL: health-related quality of life

LDDST: low-dose dexamethasone suppression test

LINAC SRS: linear LINAC system

LINAC: linear accelerator

LNSC: late-night salivary cortisol

LVP: lysine vasopressin

PMT: preoperative medical treatment

Proton-beam SRS: proton-beam system

PTCOE: Pituitary Tumor Center of Excellence

QoL: quality of life

SCRT: stereotactic conformal radiotherapy

SRS: stereotactic radiosurgery

SRT: stereotactic radiotherapy

SSTR: somatostatin receptor

TS: transsphenoidal surgery

UFC: urinary free cortisol

USP8: ubiquitin specific peptidase 8

VLDL: very-low-density-lipoprotein

Introduction

Cushing’s disease (CD) is a rare disorder caused by an adrenocorticotropin (ACTH) secreting pituitary adenoma [1]. If untreated, CD is associated with an increased morbidity and mortality, mostly due to cardiovascular and metabolic comorbidities [2] [3]. Recently, mutations in the ubiquitin specific peptidase 8 (USP8) gene have been identified in functional sporadic corticotroph adenomas causing CD [4] [5] [6] [7].

Clinical presentation, differential diagnosis and treatment of CD frequently represent a demanding task for the endocrinologist despite advances in diagnostic testing, surgical techniques and new pharmacological agents [8]. There is consensus that the best care for these patients is provided by an interdisciplinary team composed of dedicated endocrinologists and experienced pituitary surgeons working in collaboration, in a so called Pituitary Tumor Center of Excellence (PTCOE) [9].

Many typical features of hypercortisolism are highly prevalent in the general population and therefore less discriminative for CD diagnosis [10]. Clinical presentation of CD is variable, ranging from mild or subclinical hypercortisolism to moderate or severe hypercortisolism [11]. Three biochemical tests — urinary free cortisol (UFC), plasma cortisol after dexamethasone and/or late night salivary cortisol are needed to distinguish patients with Cushing’s syndrome (CS) from those with obesity or metabolic syndrome [12]. Recurrent infections and osteopenia have been reported to be the most discriminant symptoms between obesity or diabetes mellitus and CS [13].

Numerous diagnostic tests are currently available for establishing diagnosis of hypercortisolism as well as for differential diagnosis of CD. However, none of the available diagnostic tests possesses optimal sensitivity and sensibility and according to currently available consensus guidelines, a combination of two or more tests is recommended in order to establish diagnosis [10].

Transsphenoidal surgery (TS) presents the treatment of choice for CD. However, disease persistence and/or recurrence are frequent; in such cases, repeat TS, radiosurgery and/or pharmacological agents might be required [14]. Although numerous agents have been tested for CD, no optimal medical treatment exists so far, treatment side-effects are frequent and disease persistence rates are high. Bilateral adrenalectomy (BA) has proved to be effective and relatively safe in CD patients with persistent disease and/or poor biochemical control [15].

Aim of this review is to elucidate current challenges concerning CD e. g. various clinical presentation according to disease severity, present strengths and pitfalls of existing diagnostic tests, enlighten the need for new diagnostic approaches, appraise the effects of TS and currently available pharmacological agents for CD as well as recognize future perspectives regarding this challenging condition.

Signs & Symptoms

Numerous signs of CD such as buffalo hump, facial fullness, obesity, thin skin, peripheral oedema, acne and hirsutism are common in the general population, whereas signs such as easy bruising, facial plethora, proximal myopathy or proximal muscle weakness, striae rubrae and weight gain with decreasing growth velocity in children belong to the most useful features for diagnosing CD [10]. Central obesity and weight gain represent the most common and often the initial clinical manifestation of hypercortisolism (95% of patients). Chronic glucocorticoid excess can also lead to skin thinning, easy bruising or purpura resulting from even small traumas and proximal weakness due to muscle wasting. Minor wounds heal slowly and spontaneous tendon ruptures might happen. Other manifestations of CD include facial acne, hirsutism, acanthosis nigricans and hyperpigmentation. Chronic cortisol excess is also characterized by an impaired defence mechanism. Alterations in calcium metabolism result in bone loss, osteoporosis and pathological fractures associated to increased pain [16]. Bone mass can be restored over time after successful treatment for hypercortisolism [17] [18] [19].

CD is associated with numerous cortisol-dependent comorbidities such as psychiatric disorders, diabetes, hypertension, hypokalemia, infections, dyslipidemia, osteoporosis, and poor physical fitness, which lead to increased morbidity and mortality [20] [21]. A significant proportion of these comorbidities seem to persist even after long-term disease remission [22] [23] [24] [25]. According to the present Endocrine Society Clinical Practice Guideline, effective treatment of CD includes not only the normalization of cortisol levels, but also the normalization of comorbidities via directly treating the cause of CD and by correspondent treatments (e. g. antihypertensives) [26]. All patients should receive monitoring and adjunctive treatment for cortisol-dependent comorbidities throughout their lives until resolution [26]. All comorbidities should be treated aggressively and if necessary, appropriate consultations should be pursued. When CD and associated comorbidities are managed optimally, mortality rates improve; whether they are similar to those of the general population, remains questionable [26].

Direct and indirect effects of cortisol on lipolysis are believed to cause dyslipidemia in CD [27]. CD has been additionally associated with an increased prevalence of thromboembolic complications and a hypercoagulable state [28]. Glucocorticoid excess further predisposes to endocrine changes, including growth hormone deficiency, gonadal dysfunction, mild secondary hypothyroidism and thyroid nodules [29] [30].

Many CD patients (>70%) suffer from neuropsychiatric disturbances including major depression, anxiety, personality changes, mania, psychosis and sleep disorders [31] [32]. Prolonged glucocorticoid hypersecretion exacerbates cognitive aging, including decreased concentration and impaired memory, possibly linked to brain atrophy and low hippocampal volume [33] [34]. Patients with CD display significantly more often anxiety, depression and psychotic symptoms compared to healthy controls [35] [36]. Impaired quality of life (QoL) in active CD is a consistent finding in many studies and has implications for the long-term management of the disease. All health-related quality of life (HRQoL) parameters improve after treatment with TS, thus a stable long-term low QoL remains [37] [38].

Advances in Diagnostic Testing and Need for New Tests

Numerous biochemical tests have been proposed for the diagnosis of hypercortisolism; however, their diagnostic accuracy depends upon etiology of hypercortisolism, patient’s comorbidities, robustness of the assays, concomitant medications and the setting of investigations [39].

Patients with multiple features compatible with hypercortisolism should be initially tested with one test of high diagnostic accuracy e. g. UFC, late night salivary cortisol, 1 mg overnight or 2 mg 48-h dexamethasone suppression test. If initial testing is abnormal, patients should receive a second confirmatory test and then undergo testing for the cause of CS [10]. The standard tests to differentiate between CD and ectopic CS comprise the CRH-stimulation test with a sensitivity of 76% and a specificity of 100% and the HDDST with a sensitivity of 88% and a specificity of 90% [40].

However, diagnostic reality seems to differ from available guidelines, as shown in a recent publication from the European Registry on CS (ERCUSYN) [39]. Of the first-line tests, UFC was performed in 78% of patients, overnight 1 mg dexamethasone suppression test in 60% and late-night salivary cortisol in 25%. Use of high-dose dexamethasone suppression test (HDDST) was slightly more frequent in the last 5 years as compared with previous years. Of the additional tests, late-night serum cortisol was measured in 62% and 48-h 2 mg/day low-dose dexamethasone suppression test (LDDST) in 33% of cases. ACTH was performed in 78% of patients.

As far as CD diagnosis is concerned, a cutoff of preoperative ACTH/cortisol ratio>2.5 was recently suggested to be diagnostic of CD with a sensitivity of 63% and a specificity of 82% [41]. However, this new preoperative ratio is not well established and can be used to diagnose CD only together with other diagnostic tests. Additionally, we have to take into account that the standard CRH-stimulation test with a sensitivity of 76% and a specificity of 100% and the HDDST with a sensitivity of 88% and a specificity of 90% are rather superior [40]. On the other hand, an ultrasensitive late night salivary cortisol assay by tandem mass spectrometry (LC-MS/MS) was recently found to have diagnostic sensitivity of 100% and specificity of 92% - when the cutoff value was 70 ng/dL - in determining patients with CS or CD [42]. The desmopressin test - a vasopressin analogue selective for type 2 vasopressin receptors – has been recently suggested as a valid tool both in the diagnosis and in the follow-up of patients with CD [43].

In the differential diagnosis of ACTH-dependent CS, bilateral inferior petrosal sinus sampling (BIPSS) is useful in cases when there is no obvious source of ACTH hypersecretion, sellar imaging fails to detect small pituitary adenomas or a pituitary incidentaloma might be present [44] [45]. Standardized cut-off value for inferior petrosal sinus to peripheral venous ACTH≥2:1 for the basal and ≥3:1 after stimulation are considered to imply a pituitary source of ACTH excess. However, diagnostic errors exist, false negative cases have been described and many patients assumed to have ectopic tumors based upon negative BIPSS remain without diagnosis as described in a retrospective study by Swearingen et al.; the authors report a sensitivity of 90% with a specificity of 67% after CRH stimulation [46]. On the other hand, BIPSS using either human corticotropin-releasing hormone (hCRH) or lysine vasopressin (LVP) stimulation confirmed the ACTH source in all patients [47]. BIPSS with desmopressin has been recently proposed as an alternative choice to IPSS with CRH, however with moderate accuracy in tumor lateralization (concordance rate 72.5%) [48].

Data regarding sensitivity and sensibility of biochemical tests in obese populations are rather conflicting. Recently, sensitivity of the late-night salivary cortisol (LNSC) measured by automated electrochemiluminescence immunoassay (ECLIA) was found to be low in detecting CD in an obese population (BMI+≥ 35 kg/m²) [49]. An automatic face classification of hypercortisolism by computer software has been even suggested as a novel screening approach in women [50].

In pregnancy, another real medical challenge as far as diagnosis and management of CD are concerned, the hypothalamus-pituitary-adrenal (HPA)-axis undergoes significant changes and symptoms of hypercortisolism are difficult to distinguish from those of pregnancy; on the other hand, there is no consensus regarding the most effective and safe treatment modality under these exceptional circumstances [51].

Therapy

Primary goals of CD treatment comprise normalization of cortisol secretion, ablation or disruption of the primary tumor lesion, preservation of the anterior pituitary function and reversal or amelioration of clinical complications. Patients’ conditions need to be controlled for a long period of time to prevent recurrence [52] [53]. A multimodal approach is often required to achieve an efficacious disease management [52].

A schematic algorithm for the management of CD is shown in [Fig. 1].

Fig. 1 Schematic algorithm for the management of Cushing̛s Disease.

Outcome of TS

TS presents the treatment of choice for CD. Remission rates vary dependent on tumor size (65–90% for microadenomas;<65% for macroadenomas), tumor extension, adenoma visibility on magnetic resonance imaging, and neurosurgical expertise [14] [54]. Extensive follow up after TS is essential for at least 10 years due to high recurrence risk of 20–25% [55] [56] [57]. Disease persistence or recurrence requires second-line treatment, which includes repeat surgery, radiotherapy, pharmacological therapy and adrenalectomy. However, none of these alternatives is free of complications. Repeat surgery has generally a lower rate of success than first surgery (50–60%) and bears an increased risk of pituitary failure [53] [58] [59].

In a single-center experience, 341 patients undergoing first TS had a remission rate of 86% for macroadenomas and 83% for microadenomas, lower remission rates for second TS and even lower for patients with invasive tumors [60]; outcomes were obtained with a follow-up length from 12 to 36 months.

We also attempted to describe long-term remission and recurrence rates of CD in a series incorporating different neurosurgeons, trying to reflect care reality in the Munich Metropolitan Region. After first TS, we recorded an overall remission rate of 71% comparing favorably with the literature; patients with macroadenomas experienced lower remission rates compared to those with microadenomas (69% vs. 79%), again in accordance with published series. We documented an overall recurrence rate of 34%, which falls at the higher end of the published range so far, supporting our study hypothesis (series incorporating different neurosurgeons vs. single-surgeon expert series) [54].

Whether remission and recurrence rates differ according to surgical technique remains under debate. A recently published meta-analysis found no significant difference regarding remission and recurrence rates between patients who underwent endoscopic and those who underwent microscopic TS [61]. Patients with confirmed CD and no adenoma at the time of TS represent an additional challenge for the neurosurgeon. Carr et al. documented a beneficial effect of a two-thirds pituitary gland resection when no adenoma was found at the time of TS [62], while Cebula et al. found no statistical difference between patients with positive or negative MRI [63].

Radiotherapy & bilateral adrenalectomy

Radiotherapy should be considered as second-line treatment for patients with persistent hypercortisolism after pituitary surgery or as a primary treatment in those unfit for surgery. Two different modalities have been employed for radiotherapy in CD patients, named conventional photon beam radiotherapy (CRT) and stereotactic radiotherapy (SRT). CRT was the first radiation treatment available for CD. It consists in delivering radiation treatment with photons generated by a linear accelerator (LINAC) to the target tumor at daily doses over a period of 25–30 days to provide nontumor cells time to recover between doses [52]. SRT substituted recently CRT, because it can deliver a high dose of radiation to the tumor by minimizing the exposure of surrounding structures [52] [64]. SRT can be delivered as single treatment (stereotactic radiosurgery [SRS], that is safer for tumors distant more than 3–4 mm from the optic apparatus) or fractionated treatment (stereotactic conformal radiotherapy [SCRT]). SRS can be performed with different techniques, including a multiheaded cobalt unit (GammaKnife [GK]), a linear LINAC system [LINAC SRS], or a proton-beam system [Proton-beam SRS] [48] [64]. The latter, has the advantage of redistributing the radiation dose to a three-dimensional target maximizing the exclusion of the surrounding normal tissue [64].

The outcome of radiotherapy in CD is based on control of hormone secretion and tumor growth. A wide experience has been documented with the CRT, and more recently data have been accumulated about SRT. In both cases, remission of hypercortisolism can be reached with a variable interval, and no clear difference in time of decline of cortisol levels was detected so far [64] [66]. However, more long-term follow up studies are needed to detect the possibility of recurrence after SRT [52].

Studies showed that radiotherapy is associated with disease control in an average of 64% of patients by using CRT and 61% with different approaches of SRT, and recurrence was reported in around 16% and 12% of patients for CRT and SRT, respectively [52]. Despite the efficacy of the treatment, there are severe risks associated that include pituitary failure in 50% of cases [53], optic neuropathy (1–2%) and other cranial neuropathies (2–4%) [65]. Recurrence was in principle reported in patients who received conventional RT [65] [67].

In case of severe and prolonged disease, an additional second-line therapy is represented by BA, which was widely used in the past. A rapid decrease in cortisol levels is obtained, but loss of adrenal function implies a lifelong dependency on glucocorticoid substitution and a risk for developing Nelson´s syndrome [68].

Medical therapy

Medical treatment can be applied at any stage of the disease, even preoperatively to reduce complications, e. g. bleeding tendency [69]. According to ERCUSYN, patients who receive preoperative medical treatment (PMT, 20%) are more likely to have normal cortisol seven days after surgery [70]. Several molecular targets are currently available, however, there is still little clinical experience [57] [71] [72] [73] [74] [75].

Mechanism of action, potential clinical usability and effects of the currently approved drugs for CD are shown in [Table 1].

Table 1 Mechanism of action, potential clinical usability and effects of the currently approved drugs for Cushing̛s Disease.

Drug	Mechanism of action	Potential clinical positioning	Beneficial effects	Side effects	References
Ketoconazole	↓ CYP17, ↓ CYP11 β	Pre-post surgery	Decrease of UFC levels	hepatoxicity	74, 75
Metyrapone	↓ CYP11 β	Pre-post surgery/radiotherapy	Decrease of UFC levels	Adrenal insufficiency, increased androgen levels	76, 77
Etomidate	↓ CYP11 β	For patients not able to take oral medication	Rapid adrenal suppression	Adrenal suppression, decrease in blood pressure, anaphylactic reactions, nausea, vomiting	74 79
Mitotane	↓ CYP11A1, ↓ CYP11 β	Pre-post surgery	Decrease of cortisol production	gastrointestinal, neurological, hepatic disturbances	55, 80
Mifepristone	GR antagonist	Non-responders to multimodal therapy	Decrease body weight, waist circumference and body fat, increased insulin sensitivity	Nausea, fatigue, decrease of blood potassium, headaches, arthralgia, vomiting, endometrial thickening, peripheral edema	74, 81 82
Pasireotide	SSTRs (mainly 5) stimulation	After surgery or in patients not eligible for surgery or with recurrence	Decrease of UFC levels	Glucose-related adverse effects	87-91
Cabergoline	D2 receptor stimulation	Mainly effective in patients with D2 expression	ACTH suppression	Well tolerated in general	52, 94
Retinoic acid	Inhibition of ACTH secretion	Persistent of recurrent hypercortisolism after trans-sphenoidal surgery	Decrease of UFC levels	Potential teratogenicity, mucocutaneous toxicity, liver function abnormalities, conjunctivitis, mucositis and severe photosensitivity	95-97

Adrenal-targeted drugs

Adrenal-directed therapy consists of drugs blocking steroidogenesis to control cortisol excess e. g. ketoconazole, metyrapone, etomidate and mitotane. Although generally very effective, they do not target the source of the disease and require close clinical monitoring due to adverse effects, including adrenal insufficiency. Steroidogenesis inhibitors can be applied before and after surgery or radiotherapy, or as bridging therapy till reaching definitive eucortisolism [52] [69] [73].

Ketoconazole is a 17-alfa-hydroxylase (CYP17A1) and 11-beta-hydroxylase (CYP11β) inhibitor; it has been extensively used in CD patients due to its potent and rapid normalisation of UFC levels. However, close liver enzyme monitoring is necessary due to potential hepatotoxicity. Small cohort studies showed UFC normalisation in 30 to 90% of patients [74]. A retrospective multicenter study showed beneficial effects of ketoconazole even when administered preoperatively (improvement in diabetes, hypertension and hypokalaemia in 50% of cases). Hepatotoxicity was relatively frequent, but remained moderate [75].

Metyrapone inhibits the final steps of steroidogenesis and is generally used as a second- or third-line agent in CD in combination with other drugs, which may help to ameliorate its side effects. Metyrapone achieved biochemical remission in 83% of CD patients, who also underwent radiotherapy. The drug was well tolerated [76]. Most common side effects are adrenal insufficiency, acne and hirsutism, hypokalemia, edema, and hypertension [77].

In cases of endocrine cancer-related life-threatening hypercortisolism, combination therapy with metyrapone and ketoconazole has proved to be well tolerated and provides rapid control of hypercortisolism and clinically relevant endpoints [78].

Etomidate is an anesthetic drug, only available for parenteral administration. It has a rapid onset of action and a similar mechanism with that of metyrapone [74]. It can be particularly useful in severely ill hospitalized or psychotic patients (rare phenomenon) to normalise hypercortisolemia rapidly [79]. Side effects include adrenal suppression, hypotension, anaphylactic reactions, nausea and vomiting.

Although mitotane is an adrenostatic drug such as ketoconazole, metopyrone or etomidate, it is above all an adrenolytic agent and therefore primarily suitable for treating patients with adrenocortical carcinoma. A biochemical response in CD patients was recently reported as first- or second line therapy [80]. Since it is very lipophilic, it is mainly stored in the adipose tissue and the brain causing long-lasting gastrointestinal, neurological and hepatic side-effects, and therefore less suitable for treating CD. Mitotane can induce adrenal insufficiency during long-term therapy [55].

Another adrenal-targeted therapeutic concept includes the blockade of glucocorticoid receptor with mifepristone [74]. In the largest prospective study to date, long-term mifepristone treatment increased ACTH in approximately two-thirds of CD patients, with stable ACTH elevations observed within the first week of treatment. Over time, both corticotroph tumor progression and regression occurred, with possible significant increases in ACTH levels without evidence of tumor growth [81]. However, reported side effects include nausea, fatigue, hypokalemia, headaches, arthralgia, vomiting, endometrial thickening and peripheral edema [82]. A limitation of mifepristone is the fact that there is no biochemical marker for its effect; the patient should be substituted with hydrocortisone for safety reasons.

Novel adrenostatic drugs are currently under investigation with promising beneficial effects. LCI699 (Osilodrostat) is an inhibitor of cortisol and aldosterone synthesis [83]. It shares a similar mechanism of action of metyrapone, but being more potent and with a longer half-life. Side effects such as gastrointestinal disturbances followed by headaches have been reported [73]. At present, phase 2 and phase 3 studies are ongoing to test safety and efficacy of the drug in CD [73] [84] [85].

Levoketoconazole (COR-003) acts similarly to its enantiomer, ketoconazole (2 S, 4 R and 2 R,4 S racemic mixture), but has superior effects on the integral enzymes in the cortisol biosynthesis pathway, possibly leading to higher efficacy at lower doses, and fewer adverse side effects [73] [83]. A phase III single-arm, open-label trial (clinicaltrials.gov; NCT01838551) is currently ongoing to evaluate the effects of levoketoconazole in patients with CS [73] [86].

Pituitary directed drugs

Targeting the corticotroph pituitary adenoma can provide a direct effect on the source of the disease. The somatostatin analogue pasireotide has a higher affinity for somatostatin receptor (SSTR) 5, which is the most abundant SSTR in human corticotroph adenomas and was demonstrated to inhibit ACTH secretion and tumor growth both in vitro and in vivo [87] [88]. The drug is approved for CD patients not eligible to surgery or with recurrence. In a phase III study (n=16, 5 years of pasireotide treatment), median percentage change from baseline in mean UFC was -82.6% and -81.8% after 1 and 5 years respectively, while 11 patients had mean UFC≤upper limit of normal after 5 years with a similar safety profile at 5 years to that reported after 12 months [89]. In the same study , significant improvements of general signs and symptoms were recorded even without complete UFC normalisation, and hyperglycemia-related events were experienced in 73% of·patients [90], confirming strong need for frequent blood glucose monitoring [91].

The dopamine agonist cabergoline has been initially tested in CD patients due to the presence of functional D2 receptor in some corticotroph tumors in vitro and in vivo, proving sufficient disease control in approximately 40% [92] [93]. No important adverse effects were observed [52]. The drug can be used as off label treatment in a small subset of CD patients, depending on tumor size, origin of the corticotroph adenoma or molecular characteristics of the D2 receptor [94].

Retinoic acid showed promising in vitro and in vivo results in terms of inhibition of tumor cell growth and hormone secretion [95] [96]. A key limitation of retinoid therapy is that concentrations required for being effective might cause teratogenicity, mucocutaneous toxicity, liver function abnormalities, conjunctivitis, mucositis and severe photosensitivity. In a proof-of-concept study, 42% of patients showed UFC decrease or normalization after 6 months; 43% of patients had full disease control, whereas 29% had partial disease control. The treatment was generally well tolerated [97].

Conclusions – Future Perspectives

Chronic glucocorticoid excess leads to numerous somatic and psychiatric comorbidities and increased mortality, which often persist despite long-term biochemical control of the disease. Clinicians should treat all comorbidities aggressively and seek for appropriate consultations, if necessary. Genetic and molecular mechanisms responsible for excess ACTH secretion have been identified. New biochemical and imaging approaches as well as progress in surgical and radiotherapy techniques have improved disease management. Development of new pharmacological agents offers physicians additional choices to treat persistent hypercortisolism; however, clinical experience with most of these compounds is limited. The best care for these chronically ill patients is provided by a multidisciplinary team composed of dedicated endocrinologists and experienced pituitary surgeons. The development of expert excellence networks including common databases and biobanking structures facilitates optimal, individualized care for patients affected by this challenging disease. Structured consultation hours are needed in order to reverse increased morbidity and mortality and identify tumor recurrence early.

Conflict of Interest

GS has received consulting honoraria, reimbursement of conferences/educational event fees, travel expenses, and/or study support (third-party funds) from Pfizer, Ipsen, Lilly, Shire, Novartis, Sandoz, NovoNordisk, and HRA. DC and CD have nothing to disclose.

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