The USP8 mutational status may predict long-term remission in patients with Cushing's disease

Cushing's disease due to somatic USP8 mutations: a systematic review and meta-analysis

PURPOSE

Cushing's disease (CD) is a severe illness generally caused by microcorticotropinomas (MICs) and in approximately 7-20% of patients by macrocorticotropinomas (MACs). USP8-mutations have been identified as a major genetic cause of CD (~ 50%). Few studies have reported the distribution between MICs-MACs related to USP8-mutations and their genotype-phenotype correlations. Therefore, we aimed to evaluate USP8-mutations in a cohort of MICs-MACs from a unique center and to perform a systematic review and meta-analysis.

METHODS

DNA-tumor-tissues from 47 corticotropinomas (16 MICs and 31 MACs) were sequenced. Clinical-biochemical data, radiological imaging data and remission/recurrence rates were evaluated. In addition, we performed a meta-analysis of nine published series (n = 630).

RESULTS

We identified four different USP8-mutations previously described, in 11 out of 47 (23.4%) corticotropinomas; 8 out of 11 were MACs. The urinary cortisol levels of our patients with corticotrophin USP8-mutated-alleles were lower than those of patients with wild-type (WT) alleles (p ≤ 0.017). The frequency of USP8-mutated-alleles among the series was approximately 30% with a higher prevalence in female-patients (p < 0.1 × 10^-4). Among the 5 series, the remission rates were higher in patients with USP8-mutated-alleles than in those with the USP8-WT-alleles (p < 0.1 × 10^-4).

CONCLUSION

Our data, as well as the retrospective review of CD series associated with USP8-mutated alleles, show heterogeneous findings among the series. Several drawbacks included the lack of a systematic protocol to evaluate these patients before surgery and follow-up. Further prospective studies using a systematic protocol will provide more consistent information about the influence of the corticotropinomas with USP8-mutated alleles on the phenotype, responses to treatment and outcome of patients with CD.

Clinical characteristics and surgical outcome in USP8-mutated human adrenocorticotropic hormone-secreting pituitary adenomas

PURPOSE

somatic mutations in the ubiquitin-specific protease 8 (USP8) gene have recently been described in patients with Cushing's disease (CD). The aim of the study is to verify whether USP8 mutation may predict early and late outcome of pituitary surgery in patients with CD operated at a single institution.

METHODS

We performed a retrospective genetic analysis of 92 adrenocorticotropic hormone (ACTH)-secreting pituitary adenomas. Specimens were screened for USP8 hotspot mutations in the exon 14 with Sanger sequencing. Hormonal and surgical data were compared between USP8 variant carriers and wild-type tumors.

RESULTS

USP8 variants were detected in 22 adenomas (23.9%) with higher prevalence in women (28.9% vs. 5.3% in men; p < 0.05). No significant difference in hormonal levels and tumoral features in relation to USP8 status was observed. Interestingly, USP8-variant carriers were more likely to achieve surgical remission than wild-type adenomas (100% vs. 75.7%; p = 0.01). Conversely, recurrence of CD occurred in 23% of USP8-mutated patients and in 13% of patients with wild-type adenoma. The recurrence-free survival did not differ significantly between the two groups (p = 0.42).

CONCLUSIONS

ACTH-secreting pituitary adenomas carrying somatic USP8 mutations are associated with a greater likelihood of surgical remission in patients operated by a single neurosurgeon. Recurrence rates are not related with USP8-variant status.

Recent advances in understanding corticotroph pituitary tumor initiation and progression

Cushing’s disease is the most frequent form of hypercortisolism and is caused by hypophyseal corticotroph adenomas secreting excessive amounts of adrenocorticotropic hormone. Most of the tumors develop sporadically and only a limited number of corticotroph adenomas have been found to be associated with different neuroendocrine syndromes or with familial isolated pituitary adenomas. The pathogenic mechanisms of corticotroph adenomas are largely unknown, but the discovered aberrant chaperoning activity of heat shock protein 90 on the one hand and the presence of ubiquitin-specific protease 8 mutations on the other hand partially explained the causes of their development. Corticotroph tumors arise initially as benign microadenomas but with time form invasively growing aggressive macroadenomas which can switch to corticotroph carcinomas in extremely rare cases. The mechanisms through which corticotroph tumors escape from glucocorticoid negative feedback are still poorly understood, as are the processes that trigger the progression of benign corticotroph adenomas toward aggressive and malignant phenotypes. This review summarizes recent findings regarding initiation and progression of corticotroph pituitary tumors.