Poster Presentation ESA-SRB 2023 in conjunction with ENSA

New histological variants of pituitary tumours vary in their patterns of expression of somatostatin receptors. (#252)

Prishila Fookeerah 1 2 , Winny Varikatt 3 4 , Mark AJ Dexter 4 5 , Mark Mclean 2 6
  1. Diabetes and Endocrinology, Westmead Hospital, Sydney, NSW, Australia
  2. School of Medicine, Western Sydney University, Sydney, NSW, Australia
  3. Department of Tissue Pathology and Diagnostic Oncology, Westmead Hospital, Sydney, NSW, Australia
  4. Westmead Clinical School, University of Sydney, Sydney, NSW, Australia
  5. Department of Neurosurgery, Westmead Hospital, Sydney, New South Wales, Australia
  6. Department of Diabetes and Endocrinology, Westmead Hospital, Sydney, NSW, Australia

Introduction

The 2022 WHO classification of pituitary neuroendocrine tumours(PitNETs) recognises 17 histological variants of pituitary tumours. These PitNETs differ in their clinical manifestations and response to medical therapy. Tumour subtypes may express somatostatin receptors (SSTR), a potential drug target to achieve tumour reduction and control of hormone secretion. There is a well-established role for somatostatin receptor ligands(SRL) in the management of acromegaly and Cushing’s disease. Previous studies have not assessed SSTR expression in the new histological variants. Our aim is to determine patterns of SSTR expression to understand differences in clinical behaviour and response.

 

Methodology

We conducted a retrospective study of PitNETs at Westmead Hospital resected from 2011 to 2018. Immunohistochemistry was performed on all tumours to evaluate expression of pituitary hormones, transcription factors(PIT1, SF1 and TPIT), co-factors (GATA3, oestrogen receptor) and somatostatin receptors (SSTR2, SSTR5). Patterns of expression of SSTR2 and 5 were assessed.

 

Results

246 pituitary tumours were included in this study. Positive SSTR2 expression was seen in 69.2% PIT1, 45.3% gonadotroph and 3.9% corticotroph tumours. The corresponding expression of SSTR5 was 67.3% of PIT1, 0.9% gonadotroph tumours and 23.5% corticotroph tumours. Among lactotroph tumours, 7.7% showed positive immunostaining for SSTR2; 38.5% expressed SSTR5. Among the histological variants that can cause acromegaly(GH-PitNETs), SSTR2 expression was seen in 94.7% and SSTR5 in 92.1%. When grade(intensity and extent) of immunoreactivity was assessed, 100% densely granulated somatotroph and mature plurihormonal PIT1 PitNETs showed strong SSTR2 expression compared to 11.1% sparsely granulated somatotroph, 50% immature PIT1 and 45.4% mammosomatotroph tumours. 95% GH PitNETs showed only weak or moderate staining for SSTR5.  

 

Conclusion

Not all GH-PitNETs strongly expressed SSTR2 or SSTR5, possibly accounting for differences in clinical response. A small proportion of corticotroph and lactotroph tumours expressed SSTR5. Our findings may be useful in predicting therapeutic response to SRL in the future.