In situ hybridization for different mRNA in GH-secreting and in inactive pituitary adenomas

Absence of immunostaining for growth hormone in a subset of patients with acromegaly

The presence of growth hormone (GH) immunostaining in patients who lack the biochemical and clinical features of acromegaly has been described. In contrast, there is little information on the absence of GH immunostaining in patients with acromegaly. We describe five patients with acromegaly with no intratumoral immunostaining for GH. We reviewed all patients undergoing surgery for acromegaly. Out of 136 patients treated surgically in a 10 year period, five (3.7%) were found to have no GH immunostaining on repetitive testing at pathological examination. Their pathology slides were re-examined by an experienced neuropathologist, along with twenty nonfunctional pituitary tumors and ten GH-positive adenomas as negative and positive controls, respectively. All patients had clinical features consistent with acromegaly and elevated baseline insulin-like growth factor-1 (IGF-1) and GH. All patients had no immunostaining for GH on multiple inspections. Of twenty patients with nonfunctional tumors, two had ≤25% staining for GH in a scattered and non-coherent pattern and the rest were negative. In all ten positive control patients >25% of the tumor cells stained diffusely for GH. All five patients achieved biochemical remission at 1.4-8 years post-op using a combination of primary surgery alone (n = 1), repeat surgery (n = 1), radiotherapy (n = 3) and/or medical therapy (n = 2). GH immunostaining of an adenoma may not be sufficient to confirm the diagnosis of acromegaly. All patients in our small series achieved remission by multimodality therapies. Further studies are needed to evaluate the significance of our observation and whether this subset of patients follows a distinct long term clinical course.

Pituitary hormone mRNA in null cell adenomas and oncocytomas by in situ hybridization comparison with immunohistochemical and clinical data

Null cell adenomas and oncocytomas are clinically inactive adenomas of the pituitary gland. They do not show any significant hormone content detectable by immunohistochemistry. This study aimed at demonstrating mRNAs for all main pituitary hormones in 32 null cell adenomas and 31 oncocytomas by non-isotopic in situ hybridization using digoxigenin-labeled oligonucleotide probes. The results were compared with immunohistochemical and clinical data. Immunohistochemistry (ABC method) was done with monoclonal antibodies against PRL, GH, FSH, LH, TSH, ACTH, alpha-subunit, and Ki-67 (mib-1). The signals for hormone production were detected in both adenoma types in a range from 42% for GH in oncocytomas to 78% for beta-FSH in null cell adenomas. However, these signals are apparently not effective on hormone production, as was shown by almost negative immunostaining. Owing to the simultaneous detection of at least two mRNAs in 78% of null cell adenomas and in 94% of oncocytomas, we assume that both tumor types originate from pluripotential precursor cells that are capable of producing various hormones. According to our data, it is unlikely that the signals influence the clinical behavior.

GH-, PRL-, POMC-, beta-TSH-, beta-LH-, beta-FSH-mRNA in gonadotroph adenomas of the pituitary by in situ hybridization in comparison with immunostaining and clinical data

In situ hybridization (ISH) enables the visualization of specific mRNA for pituitary hormones. Our collection consists of 40 surgically removed pituitary adenomas that were classified as follicle stimulating hormone/luteinizing hormone (FSH/LH) cell adenomas by structure and by immunostaining (IH) for all pituitary hormones. All forty adenomas were regarded as clinically inactive. The aim of our study was to examine nonfunctioning adenomas by ISH for demonstration of mRNAs for all pituitary hormones. The results were compared with proliferation markers, invasiveness and clinical data. ISH detected signals for all pituitary hormones at a range of 30% for prolactin (PRL) to 85% for proopiomelanocortin (POMC). mRNA for beta-FSH was detected in 70% and beta-LH mRNA in 43% of adenomas. Thirty-three percent of adenomas revealed negative mRNA detection for beta-LH but positive hormone content. The majority of adenomas (75%) expressed more than two mRNAs simultaneously, mostly the combination of POMC mRNA together with beta-FSH mRNA and one to four others. Comparison with clinical data showed no significant differences except for one adenoma with a high Ki-67 index (> 2.1% positive nuclei). This adenoma showed very high signals for PRL and beta-TSH mRNA.

Morphological characterization and subtyping of silent somatotroph adenomas

GH-producing adenomas clinically are endocrine-active tumors accompanied with acromegaly in most instances. However, GH-producing adenomas apparently unassociated with acromegaly, or so-called silent somatotroph adenomas (SSA), have recently been reported but rarely. The reported cases are characterized by normal or slightly elevated serum levels of GH but without acromegaly. Tumor cells contain moderate, trace or no GH immunoreactivity. We experienced 7 cases of SSA which were not always similar in morphology and pathogenetic mechanism. They could be further divided into the following 3 subtypes. Subtype 1 (N = 2): a moderate number of cells were immunopositive for GH, and GH mRNA was also expressed in moderate or numerous cells. Densely granulated cells were noted. It is assumed that inhibition of hormone release into circulation. Subtype 2 (N = 3): a small number of cells were immunopositive for GH, while GH mRNA was expressed in numerous tumor cells. They were sparsely granulated cells containing fibrous bodies. These findings suggest that posttranslational processing of the gene product may be defective. Subtype 3 (N = 2): Only a scattered number of cells were immunopositive for GH and GH mRNA was co-localized in immunopositive cells. They were sparsely granulated cells containing poorly developed organelles that did not resemble those of typical sparsely granulated GH cells. The findings indicate that adenoma cells are largely immature with minimal GH lineage differentiation.

An Atypical Acidophil Cell Line Tumor Showing Focal Differentiation Toward Both Growth Hormone and Prolactin Cells

We report a case of giant pituitary adenoma in a child. Computerized tomography (CT) scan revealed a suprasellar extension tumor mass with hydrocephalus. There was no clinical evidence of acromegaly, gigantism, and other hormonal symptoms. Endocrinologic studies showed within normal value of serum growth hormone (GH: 4.2 ng/mL) and slightly increased levels of prolactin (PRL: 78 ng/mL) and other pituitary hormone values were within normal range. On suppression test by bromocryptin, both GH and PRL levels were reduced. Histopathological findings revealed that the tumor consisted of predominantly chromophobic and partly eosinophilic adenoma cells. Immunohistochemical staining detected GH and PRL in a small number of distinctly different adenoma cells, respectively. Nonradioactive in situ hybridization (ISH) also showed GH and PRL mRNA expression in identical immunopositive cells. Electron microscopy (EM) demonstrated adenoma cells with moderate or small numbers of two types of dense granules and without fibrous body which are characteristic of sparsely granulated GH-cell adenomas. The adenoma does not fit into any classification but may be an atypical acidophil cell line tumor showing focal differentiation toward both GH and PRL cells.

HGH, PRL and beta HCG/beta LH gene expression in clinically inactive pituitary adenomas detected by in situ hybridization

Within our surgical collection clinically inactive pituitary adenomas represent 30.7% of all pituitary tumours. To characterize their endocrine activity we studied 40 clinically inactive pituitary adenomas with in situ hybridization (ISH) using cRNA probes labelled with 35S encoding growth hormone (GH), prolactin (PRL) and chorionic gonadotrophin (beta HCG). No tumour was associated with clinical evidence of elevated hormone secretion. A mild hyperprolactinaemia not correlated with hormone or the mRNA content of the cells was interpreted to be incidental in 11 patients. By histological analysis, immunohistochemistry (IH) and electron microscopy the adenomas were diagnosed as small cell chromophobic (n = 16) and large cell chromophobic (n = 8) adenomas, and oncocytomas (n = 16). Gene expression of one or more hormones was identified by ISH in 18 of 40 adenomas in few cells. GH and PRL gene expression was rare (GH mRNA in 3 of 40 tumours and PRL mRNA in 8 of 40 tumours) whereas in 14 of 40 adenomas beta HCG/beta LH gene expression was identified in scattered cells. Five of 40 adenomas lacking hybridization signals revealed hormones by IH. The detection of mRNA was accompanied by positive immunostaining for the respective hormones in 72%. The combination of ISH and IH reveals good evidence that the hormones are synthesized in the tumours and not taken up from the serum and stored in the cells. The two methods used together permit a more precise analysis of tumour biology than each alone.