Expression des Apoptose-Gens Noxa in malignen und benignen neuroendokrinen Tumoren des Pankreas

Abstract

Objective: The malignant behaviour of functional and non-functional neuroendocrine pancreatic tumours (PETs) is suspected when angioinvasion, invasion of neighbouring organs, frequent mitoses and a high Ki-67-Index occur. Prognosis in well-differentiated neuroendocrine carcinomas varies considerably and prognostic parameters in addition to the histological classification particularly in well-differentiated carcinomas must be established. The Noxa-gene is expressed p53-dependent and act in a proapoptotic way. It is located on the Chromosome 18q [1, 2]. Micoarray studies in gastrinomas at our laboratory revealed a significant lower expression level of the Noxa-gene. Somatic mutations were detected in human cancer and a loss of 18q is observed in patients with poor outcome [3]. Patients and Methods: RNA and DNA from 10 benign and 10 malignant PETs were isolated. As a reference pooled RNA from human islet cells was used. Direct sequencing of the Noxa-Gene was performed to rule out somatic mutations. After confirming the integrity of the isolated RNA by RT-PCR the expression level was determined by quantitative PCR with the Roche LightCycler. Sections of tumour tissue were evaluated by immunohistochemistry with a monoclonal antibody. Clinical characteristics and followup of each patient were analyzed. Results: Median age of patients (12 male/8 female) was 44 years (29–61) and these were followed for a median period of 61 months (13–193). Somatic mutations were not identified. Expression level was decreased more than 10-fold in PETs compared to the human islet cells. Expression levels in malignant PETs (> 13-fold) were significantly lower than in benign PETs (> 10-fold), (p < 0.01). PETs greater than 20mm in size and with distant metastases demonstrated decreased expression of more than 14-fold. Islet cells and neuroendocrine cells of the small intestine stained selectively and revealed a stronger Noxa signal than PETs. Conclusions: The pro-apoptotic gene Noxa is downregulated in PETs. The decreased expression level correlates with malignancy, larger tumour size and metastatic disease. Noxa represents a possible prognostic factor in PETs. Protein expression levels could also be visualised by immunohistochemistry.