Transcriptomic dysregulation in aggressive and malignant prolactin tumours

Pituitary tumours are generally benign. However, many are invasive and some of these are aggressive with high proliferation and recurrence rates. Only metastatic tumours are considered malignant and are rare (0.2%). To identify molecular events associated with the aggressive and malignant phenotypes, we combined a comparative genomic hybridization and transcriptomic analysis of 13 prolactin (PRL) tumours classified as non-invasive (NI; n=5), invasive (I; n=2) or aggressive-invasive (AI; n=6). Each tumour showed copy number alterations which appeared to be varied and discrete in the NI and I tumour groups, and more numerous and extensive in the AI tumour group. Allelic loss within the p arm region of chromosome 11 was detected in five of the AI tumours. This region contains the cytobands 11p15.2, 11p15.1, 11p14.3, 11p14.2, 11p14.1, 11p13, 11p12 and 11p11.2. Furthermore, an allelic loss in the 11q arm was also observed in three of these five tumours, which were considered malignant based on the presence of metastases. The comparison of genomic and transcriptomic data showed that allelic loss impacted upon the expression of genes located in the imbalanced region. An original data filtering strategy allowed us to highlight five genes (DGKZ, CD44, TSG101, GTF2H1 and HTATIP2), within the missing 11p region, potentially responsible for triggering the aggressive and malignant phenotypes of PRL tumours. Our novel combined genomic and transcriptomic analysis underlines the importance of chromosome 11 allelic loss in aggressive and malignant PRL tumours and led us to propose a new strategy to find markers of progression in rare tumours. Transcriptomic analysis of Codelink Human Whole Genome Bioarray was performed for 13 prolactin tumors: 6 aggressive-invasive, 2 invasive, and 5 non-invasive.