DNA methylation of Tumour Suppressor Genes in Pituitary Neuroendocrine Tumours.

Context: Epigenetic alterations may play a role in the development and behaviour of Pituitary Neuroendocrine Tumours (PitNETs).

Objective: To evaluate the effect of methylation of Tumour Suppressor Genes (TSGs) in their gene expression and in the behaviour of PitNETs.

Material and Methods: We use MS-MLPA and q-RT-PCR techniques to analyse the DNA-promoter hypermethylation and the gene expression of 35 TSGs in 105 PitNETs. We define functionality, size and invasiveness of tumours according to their clinical manifestations, Hardy's classification and MRI invasion of the cavernous sinus, respectively.

Results: We observed different methylation patterns among PitNET subtypes. CASP8 was the most hypermethylated gene in all PitNET subtypes. The methylation status of TP73 correlated negatively with their gene expression in the overall series (p=0.013) and in some subtypes. MSH6 and CADM1 showed higher methylation frequency in macro than in microadenomas in the overall series and in corticotroph PitNETs (all p≤0.053). ESR1 and RASSF1 were higher methylated in non-invasive than in invasive tumours in the overall series (p=0.054 and p=0.031, respectively) and in the gonadotroph subtype (sGT) (p=0.055 and p=0.050, respectively). ESR1 and CASP8 appeared more hypermethylated in functioning than in sCT (p=0.034 and p=0.034, respectively).

Conclusions: DNA-methylation of TSGs has a selective effect on their gene expression and on the growth and invasiveness of PitNETs. Its involvement in their functionality is biased because all silent operated tumours are macroadenomas while all operated microadenomas are functioning ones. Therefore, the subtypes of PitNETs should be considered as different entities.