Evaluation of Expression of Somatostatin Receptor 1, 2, 3, 5 and Dopamine D2 Receptor in Spindle Cell Oncocytomas of Posterior Pituitary

Purpose: Spindle cell oncocytomas (SCOs) are very rare tumors of the posterior pituitary with potential for locally aggressive behaviour. Their treatment includes surgery and possibly radiotherapy, however other options are lacking. Somatostatin receptors (SSTs) are a possible therapeutic target for somatostatin analogues and their expression has been demonstrated recently in closely related pituicytomas, but there are no data about their presence in SCOs.

Methods: We collected five cases of SCO from four patients including one recurrent case. Immunohistochemical detection of TTF1, GFAP, CD68, SST, SST, SST, SST and D2 dopamine receptor (D2DR) was performed. Intensity, percentage of positive cells and pattern of expression was evaluated in semiquantitative fashion. Protein expression of SST and D2DR was further evaluated by western blot.

Results: Mean patient age was 61.8 years (range 47-71 years) with male to female ratio 1:1. In one patient, samples from the original tumor and its recurrence 16 years later were assessed. TTF1 was positive in all five cases, no expression of GFAP and CD68 was seen. Immunohistochemical expression of SST was noted in 1/5 cases, SST in 2/5 cases, including recurrent case but not the original case. SST was expressed in 3/5 tumors and D2 dopamine receptor in 4/5 cases. Western blot was successfully performed in four samples. SST, SST and D2DR expression was identified in all the samples, including two cases originally negative for SST and one case negative for SST by immunohistochemistry. The number of positive cells and level of expression varied among different areas of the same tumors. No expression of SST was observed. In the patient with the recurrent tumor, intensity of SST, SST and D2DR expression varied between original tumor and its recurrence.

Conclusions: We demonstrated presence of different SST subtypes and D2DR in spindle cell oncocytomas. The most commonly expressed subtype was SST and SST, while no expression of SST was observed. Expression showed spatial heterogeneity and temporal changes as seen in the recurrent case. The biological meaning of SSTs expression in SCOs is unclear as well as whether it may be exploited in treatment of selected cases.