Immunohistochemical study on so-called follicular cells and folliculostellate cells in the human adenohypophysis

New insights into the role and origin of pituitary S100β-positive cells

In the anterior pituitary, S100β protein (S100β) has been assumed to be a marker of folliculo-stellate cells, which are one of the non-hormone-producing cells existing in the parenchyma of the adult anterior lobe and are composed of subpopulations with various functions. However, recent accumulating studies on S100β-positive cells, including non-folliculo-stellate cells lining the marginal cell layer (MCL), have shown the novel aspect that most S100β-positive cells in the MCL and parenchyma of the adult anterior lobe are positive for sex determining region Y-box 2 (SOX2), a marker of pituitary stem/progenitor cells. From the viewpoint of SOX2-positive cells, the majority of these cells in the MCL and in the parenchyma are positive for S100β, suggesting that S100β plays a role in the large population of stem/progenitor cells in the anterior lobe of the adult pituitary. Reportedly, S100β/SOX2-double positive cells are able to differentiate into hormone-producing cells and various types of non-hormone-producing cells. Intriguingly, it has been demonstrated that extra-pituitary lineage cells invade the pituitary gland during prenatal pituitary organogenesis. Among them, two S100β-positive populations have been identified: one is SOX2-positive population which invades at the late embryonic period through the pituitary stalk and another is a SOX2-negative population that invades at the middle embryonic period through Atwell's recess. These two populations are likely the substantive origin of S100β-positive cells in the postnatal anterior pituitary, while S100β-positive cells emerging from oral ectoderm-derived cells remain unclear.

Follicular cells in pituitary neuroendocrine tumors

Follicular cells (FCs) are thought to be agranular, non-hormone-producing stellate cells distributed throughout the adenohypophysis, occasionally arranged around colloid-filled follicles, and thought to be more prominent in the vicinity of necrosis and apoptotic cells. A distinct but similar cell type, the folliculostellate cell (FSC), is a sustentacular cell that is negative for keratins and stains for S100, GFAP, and SOX10. While several studies have examined FSCs in pituitary neuroendocrine tumors (PitNETs), the distribution and derivation of FCs in these lesions is unclear. We examined the presence and distribution of FCs in 104 PitNETs obtained by trans-sphenoidal surgery, using immunohistochemistry for keratins as well as the full complement of immunohistochemical stains for tumor characterization. The tumors included 9 somatotroph, 5 mammosomatotroph, 7 lactotroph, 7 immature PIT1-lineage, 2 acidophil stem cell, 17 corticotroph, 53 gonadotroph, 2 null cell, and 2 unusual plurihormonal tumors. CK-positive FCs were only identified in gonadotroph PitNETs and were found in 12 (23%) of those tumors; all other tumor types were negative for FCs. FCs express keratins identified by CAM5.2, AE1/AE3, CK18, and CK19 antibodies. FCs were identified scattered singly among hormone-producing neuroendocrine cells, in small clusters of 3-5 cells and surrounding colloid-filled follicles, as well as linearly along intratumoral blood vessels. Sequential stains showed that FCs express nuclear SF1 and GATA3, transcription factors of gonadotrophs, and multiplex immunohistochemistry confirmed colocalization of SF1 in the nucleus of keratin-positive FCs. In this series, FCs were exclusively found in gonadotroph PitNETs and occurred in 23% of those tumors. Co-expression of gonadotroph transcription factors in FCs supports the concept of cellular plasticity and transformation of neoplastic hormone-producing neuroendocrine cells to FCs. Further studies are required to determine if and why gonadotrophs alone undergo this transformation, the function of these cells and whether they have prognostic value.

Co-expression of intermediate filaments glial fibrillary acidic protein and cytokeratin in pituitary adenoma

PURPOSE

To analyze the co-expression of the intermediate filaments GFAP and cytokeratin in 326 pituitary adenomas with regard to the distribution pattern, the subtype of the adenoma and clinical prognostic data.

METHODS

Tissue from 326 pituitary adenomas and 13 normal anterior pituitaries collected in the Institute of Neuropathology, University Medical Center Hamburg-Eppendorf, between 2006 and 2009 was investigated by immunohistochemistry, immunofluorescence and electron microscopy.

RESULTS

Co-expression of intermediate filaments GFAP and cytokeratin was associated with hormone expression in 62/278 cases (22%), but only found in 2/48 (4%) of null cell adenomas (p < 0.01). Simultaneous co-expression of GFAP and cytokeratin in the same cells was demonstrated in 26 out of 326 pituitary adenomas and in all 13 pituitaries. In pituitary intermediate filaments were demonstrated in a larger area of the cytoplasm than in adenoma (p < 0.01), however, overlapping expression was seen in 2.6% of the total area in both, pituitary and adenoma. Congenially, cells with overlapping expression were found near vessels and in follicles. Furthermore, adenomas with cellular co-expression of GFAP and cytokeratin were associated with a lower recurrence rate (7.7%) compared to adenomas without co-expression of intermediate filaments (17.8%).

CONCLUSIONS

Cellular co-expression of the intermediate filaments GFAP and cytokeratin in pituitary adenomas and the pituitary was demonstrated and shown to be associated with hormone expression and low recurrence rate. The results are discussed with regard to the biology of folliculostellate cells, neural transformation and tumor stem cells. This study may complement the understanding of pituitary adenoma biology.

Stem Cell Transcription Factor Sox2 Is Expressed in a Subset of Folliculo-stellate Cells of Growth Hormone-Producing Pituitary Neuroendocrine Tumours and Its Expression Shows No Association with Tumour Size or IGF1 Levels: a Clinicopathological Study of 109 Cases

Sox2 is one of the transcription factors responsible for the maintenance of stem cell phenotype. It has been implicated as a marker of stem cells in normal pituitaries and pituitary neuroendocrine tumours. To explore the clinical significance of Sox2 expression in histological sections, we performed immunohistochemical detection of Sox2 in 113 pituitary neuroendocrine tumours from 109 patients with acromegaly. In 11 tumours, we performed double immunostaining for Sox2, annexin A1 and S100 protein. Tumours were characterised using the WHO classification system. Proliferative activity and invasion were assessed. The amount of immunoreactive cells was evaluated and correlated with tumour size and biochemical features (levels of IGF1, GH, prolactin, βTSH). Sox2⁺ cells were identified in 35/38 normal pituitaries adjacent to the tumours. In 36 tumours (33%), ≥ 1% of the cells expressed Sox2, in 24 cases (22%), Sox2⁺ cells comprised < 1% and 49 cases (45%) were negative. We found no significant differences between Sox2⁺ and Sox2^- groups with respect to the age, initial levels of GH, IGF1, prolactin, βTSH, tumour size, invasion, proliferative activity or histological features. We observed a positive correlation between Sox2⁺ cell count and βTSH immunoreactive cells (r = 0.459, p < 0.001) that was further verified by multivariate analysis. Using double stain, the majority of Sox2⁺ cells coexpressed annexin A1 (average 89%) and S100 protein (average 76.2%) and showed morphological features of folliculo-stellate cells. Sox2⁺ cells are thus commonly present in growth hormone-producing tumours and normal pituitaries, and their amount does not have any prognostic significance. Most of these cells represent a subpopulation of folliculo-stellate cells, pointing out to their role as a possible stem cell population.

Epithelial and organ-related marker expression in pituitary adenomas

The histologic expression of epithelial and organ-related immunohistochemical markers in primary sellar region tumors has received little attention to date. This lack of empirical data may lead to mistaken assumptions in the evaluation of sellar region neoplasms. To address this issue, the frequency and specificity of epithelial (cytokeratin 7(CK7), CK20) and organ-related differentiation markers (gross cystic disease fluid protein-15 (GCDFP-15), thyroid transcription factor-1 (TTF-1), Napsin A, paired box 8 (PAX-8), hepatocyte paraffin 1 (HepPar1) and estrogen receptor (ER)) were studied in 40 patients with adenomas comprising five hormonal sub-types. Non-parametric statistical procedures were used to examine associations between marker expression and tumor sub-type. CK7 and CK20 immunoreactivity were seen in 48% and 8% of tumors, respectively, although never in a diffuse pattern. CK20 expression was nearly exclusive to corticotrophs, whereas CK7 frequently highlighted cells with dendritic-type morphology. The specificity of organ-related differentiation markers was 100% (monoclonal Napsin A, GCDFP-15 and TTF-1), 97% (HepPar1 and PAX-8), 90% (polyclonal Napsin A) and 72% (ER); no tumors demonstrated significant co-expression of these organ-related markers with either CK7 or CK20. The first major conclusion of this study is that CK7 staining in adenoma is more frequent than has been previously than has been previously described. CK7 immunoreactive cells often displayed a dendritic-type morphology, including within large macroadenomas, which raises the question as to whether these represent tumor cells with folliculo-stellate cell-type differentiation, as these also have dendritic cell-type morphology and express CK7 in non-neoplastic glands. The second major conclusion, which confirms earlier findings, is that CK20 staining is a very infrequent immunohistochemical finding in adenomas that is virtually limited to corticotrophs and thus is helpful in diagnostic confirmation of that sub-type. The final conclusion is in regard to those features that separate adenomas from sellar region metastases: adenomas do not demonstrate significant expression of TTF-1, monoclonal Napsin A, PAX-8, HepPar1 or GCDFP-15, nor do they exhibit diffuse expression of CK7 and CK20.

Characterization of the autoimmune response against the nerve tissue S100β in patients with type 1 diabetes

Type 1 diabetes results from destruction of insulin-producing beta cells in pancreatic islets and is characterized by islet cell autoimmunity. Autoreactivity against non-beta cell-specific antigens has also been reported, including targeting of the calcium-binding protein S100β. In preclinical models, reactivity of this type is a key component of the early development of insulitis. To examine the nature of this response in type 1 diabetes, we identified naturally processed and presented peptide epitopes derived from S100β, determined their affinity for the human leucocyte antigen (HLA)-DRB1*04:01 molecule and studied T cell responses in patients, together with healthy donors. We found that S100β reactivity, characterized by interferon (IFN)-γ secretion, is a characteristic of type 1 diabetes of varying duration. Our results confirm S100β as a target of the cellular autoimmune response in type 1 diabetes with the identification of new peptide epitopes targeted during the development of the disease, and support the preclinical findings that autoreactivity against non-beta cell-specific autoantigens may have a role in type 1 diabetes pathogenesis.

Decrease of serum S100B during an oral glucose tolerance test correlates inversely with the insulin response

Increased S100B serum levels have been considered as a marker of glial pathology, brain damage, and blood-brain-barrier impairment. However, S100B expression has also been detected outside the nervous system, suggesting that altered S100B serum levels may not exclusively reflect brain-specific pathologies. Notably, S100B secretion in adipocytes seems to be down-regulated by insulin, and up-regulated by stress and fasting. Therefore, we assumed that dynamic changes of S100B could be observed by challenging healthy subjects with an oral glucose tolerance test (OGTT). OGTT was performed in 17 healthy adult test persons (9 male and 8 female). Apart from S100B, glucose, free fatty acids, insulin, C-peptide, and cortisol were determined in all samples after an overnight fast (0 h), as well as 1h and 2h after ingestion of 75 g glucose. Mean S100B concentrations decreased about 20% during the first hour after glucose ingestion (P<0.001). This decrease of S100B levels was not related to the declining morning peak of cortisol. However, the decrease of serum-S100B 1h after glucose ingestion correlated inversely with the respective changes of serum-insulin (r = -0.484, P=0.049) and serum-C-peptide (r = -0.570, P = 0.017). Our study suggests an inverse correlation between insulin secretion and S100B release after a standardized OGTT. Additional experiments, including the administration of insulin and the measurement of other food intake-related factors are important to ascertain an insulin-regulated S100B release in vivo. To improve comparability between clinical studies assessing conditions with rather mild changes of serum S100B, blood should be taken in a more standardized way (e.g., after fasting overnight).

Stem cells and cancer stem-like cells in endocrine tissues

Cancer stem-like cells are a subpopulation of self-renewing cells that are more resistant to chemotherapy and radiation therapy than the other surrounding cancer cells. The cancer stem cell model predicts that only a subset of cancer cells possess the ability to self-renew and produce progenitor cells that can reconstitute and sustain tumor growth. Evidence supporting the existence of cancer stem-like cells in the thyroid, pituitary, and in other endocrine tissues is rapidly accumulating. These cells have been studied using specific biomarkers including: CD133, CD44, Nestin, Nanog, and aldehyde dehydrogenase enzyme. Putative cancer stem-like cells can be studied in vitro using serum-free media supplemented with basic fibroblast growth factor and epidermal growth factor grown in low attachment plates or in extracellular matrix leading to sphere formation in vitro. Cancer stem-like cells can also be separated by fluorescent cell sorting and used for in vitro or in vivo studies. Injection of enriched populations of cancer stem-like cells (also referred to as tumor initiating cells) into immunodeficient mice results in growth of xenografts which express cancer stem-like biomarkers. Human cancer stem-like cells have been identified in thyroid cancer cell lines, in primary thyroid cancers, in normal pituitary, and in pituitary tumors. Other recent studies suggest the existence of stem cells and cancer stem-like cells in endocrine tumors of the gastrointestinal tract, pancreas, lungs, adrenal, parathyroid, and skin. New discoveries in this field may lead to more effective therapies for highly aggressive and lethal endocrine cancers.

Morphometric analysis of the human anterior pituitary's folliculostellate cells during the aging process

Folliculostellate cells represent non-endocrine cells of the anterior pituitary which influence the function of the endocrine cells via paracrine action. Though there is a lack of literature data on their presence during human aging, the aim of this research was to perform the quantification of anterior pituitary folliculostellate cells by the application of immunohistochemical and morphometric methods. The material for the study consisted of 15 anterior pituitaries taken from cadavers at routine autopsy. Their tissue was processed by standard histological procedure and the obtained histological slices were stained by S100 polyclonal antibody. Digital images of stained histological sections were analyzed by morphometric method with ImageJ system. The volume density of S100 positive cells was measured for each case. Results of morphometric and statistical analysis showed a significantly positive correlation between folliculostellate cell volume density and the age of the evaluated cases. Linear regression additionally showed that the age significantly predicts folliculostellate cells volume density in our sample. Further, all cases were classified into three age groups and One Way ANOVA showed that the volume density of folliculostellate cells was significantly higher only in the third age group in relation to the first and the second group, respectively. Volume densities of the first and the second age groups were not significantly different. So, the results of our study pointed to the conclusion that folliculostellate cells presence generally increases with age, but this increase is significant only in the oldest cases and might represent the modality of successful anterior pituitary aging.

Expression of aromatase in radial glial cells in the brain of the Japanese eel provides insight into the evolution of the cyp191a gene in Actinopterygians

The cyp19a1 gene that encodes aromatase, the only enzyme permitting conversion of C19 aromatizable androgens into estrogens, is present as a single copy in the genome of most vertebrate species, except in teleosts in which it has been duplicated. This study aimed at investigating the brain expression of a cyp19a1 gene expressed in both gonad and brain of Japanese eel, a basal teleost. By means of immunohistochemistry and in situ hybridization, we show that cyp19a1 is expressed only in radial glial cells of the brain and in pituitary cells. Treatments with salmon pituitary homogenates (female) or human chorionic gonadotrophin (male), known to turn on steroid production in immature eels, strongly stimulated cyp19a1 messenger and protein expression in radial glial cells and pituitary cells. Using double staining studies, we also showed that aromatase-expressing radial glial cells exhibit proliferative activity in both the brain and the pituitary. Altogether, these data indicate that brain and pituitary expression of Japanese eel cyp19a1 exhibits characteristics similar to those reported for the brain specific cyp19a1b gene in teleosts having duplicated cyp19a1 genes. This supports the hypothesis that, despite the fact that eels also underwent the teleost specific genome duplication, they have a single cyp19a1 expressed in both brain and gonad. Such data also suggest that the intriguing features of brain aromatase expression in teleost fishes were not gained after the whole genome duplication and may reflect properties of the cyp19a1 gene of ancestral Actinopterygians.

Pituitary blastoma: a unique embryonal tumor

Pituitary blastoma, a recently described tumor of the neonatal pituitary, exhibits differentiation to Rathke epithelium and adenohypophysial cells of folliculostellate and secretory type, a reflection of arrested pituitary development and unchecked proliferation (Scheithauer et al. in Acta Neuropathol 116(6):657-666, 2008). Herein, we report the pathologic features of three additional cases, all ACTH-producing. One involved a 9-month-old male presenting with progressive right ophthalmoplegia, MRI findings of a large suprasellar mass with cavernous sinus invasion, and elevated plasma ACTH levels. The second was nonfunctioning and occurred in a 13-month-old female with right third nerve palsy. The third had been previously published as a "pituitary adenoma" in a 2-year-old female (Min et al. in Pathol Int 57(9):600-605, 2007). The subtotally resected tumors were subject to histochemical, immunohistochemical and, in two cases, ultrastructural study. Histologically, the complex tumors consisted of glands of varying from rosettes to glandular structures resembling Rathke epithelium, small undifferentiated-appearing cells (blastema), and large secretory cells. Mucin-producing goblet cells were noted in case 3. Cell proliferation was high in two cases and low in case 3. Immunoreactivity of the secretory cells included synaptophysin, chromogranin, various keratins and, to a lesser extent, ACTH and beta endorphin. MGMT immunolabeling was 40-60%. Mitotic activity was moderate to high in cases 1 and 2 and was low in case 3. The same was true for MIB-1 labeling. Germ cell markers were lacking in all cases. One tumor ultrastructurally consisted of three cell populations including (a) small, polyhedral, primitive-appearing cells (blastema) with scant cytoplasm, abundant glycogen and few organelles, (b) folliculostellate cells and (c) large corticotroph cells containing rough endoplasmic reticulum, golgi membranes, spherical, 150-400 nm secretory granules and occasional perinuclear, intermediate filament bundles. A second example (case 3) lacked a blastema and glandular component. The clinical and morphologic features of our three cases were those of pituitary blastoma. The finding of cellular elements of adenohypophysial development is consistent with a diagnosis of pituitary blastoma and aligns it with blastomas of other organs. It also suggests an underlying specific genetic abnormality. Marked variations in cellular proliferative activity suggest blastomas occur in low- and higher-grade form. Variable MGMT reactivity suggests an incomplete response to temozolomide therapy. Literature regarding similar morphologically complex, infantile, Cushing disease-associated lesions is briefly reviewed.

Ectopic sphenoid sinus pituitary adenoma (ESSPA) with normal anterior pituitary gland: a clinicopathologic and immunophenotypic study of 32 cases with a comprehensive review of the english literature

Ectopic sphenoid sinus pituitary adenoma (ESSPA) may arise from a remnant of Rathke's pouch. These tumors are frequently misdiagnosed as other neuroendocrine or epithelial neoplasms which may develop in this site (olfactory neuroblastoma, neuroendocrine carcinoma, sinonasal undifferentiated carcinoma, paraganglioma, melanoma). Thirty-two patients with ESSPA identified in patients with normal pituitary glands (intact sella turcica) were retrospectively retrieved from the consultation files of the authors' institutions. Clinical records were reviewed with follow-up obtained. An immunohistochemical panel was performed on available material. Sixteen males and 16 females, aged 2-84 years (mean, 57.1 years), presented with chronic sinusitis, headache, obstructive symptoms, and visual field defects, although several were asymptomatic (n = 6). By definition, the tumors were centered within the sphenoid sinus and demonstrated, by imaging studies or intraoperative examination, a normal sella turcica without a concurrent pituitary adenoma. A subset of tumors showed extension into the nasal cavity (n = 5) or nasopharynx (n = 9). Mean tumor size was 3.4 cm. The majority of tumors were beneath an intact respiratory epithelium (n = 22), arranged in many different patterns (solid, packets, organoid, pseudorosette-rosette, pseudopapillary, single file, glandular, trabecular, insular). Bone involvement was frequently seen (n = 21). Secretions were present (n = 16). Necrosis was noted in 8 tumors. The tumors showed a variable cellularity, with polygonal, plasmacytoid, granular, and oncocytic tumor cells. Severe pleomorphism was uncommon (n = 5). A delicate, salt-and-pepper chromatin distribution was seen. In addition, there were intranuclear cytoplasmic inclusions (n = 25) and multinucleated tumor cells (n = 18). Mitotic figures were infrequent, with a mean of 1 per 10 HPFs and a <1% proliferation index (Ki-67). There was a vascularized to sclerotic or calcified stroma. Immunohistochemistry highlighted the endocrine nature of the tumors, with synaptophysin (97%), CD56 (91%), NSE (76%) and chromogranin (71%); while pan-cytokeratin was positive in 79%, frequently with a dot-like Golgi accentuation (50%). Reactivity with pituitary hormones included 48% reactive for 2 or more hormones (plurihormonal), and 33% reactive for a single hormone, with prolactin seen most frequently (59%); 19% of cases were non-reactive. The principle differential diagnosis includes olfactory neuroblastoma, neuroendocrine carcinoma, melanoma, and meningioma. All patients were treated with surgery. No patients died from disease, although one patient died with persistent disease (0.8 months). Surgery is curative in the majority of cases, although recurrence/persistence was seen in 4 patients (13.8%). In conclusion, ESSPAs are rare, affecting middle aged patients with non-specific symptoms, showing characteristic light microscopy and immunohistochemical features of their intrasellar counterparts. When encountering a tumor within the sphenoid sinus, ectopic pituitary adenoma must be considered, and pertinent imaging, clinical, and immunohistochemical evaluation undertaken to exclude tumors within the differential diagnosis. This will result in accurate classification, helping to prevent the potentially untoward side effects or complications of incorrect therapy.

Intrapituitary expression and regulation of the gp130 cytokine interleukin-6 and its implication in pituitary physiology and pathophysiology

Interleukin (IL)-6, a member of the gp130 cytokine family, is sometimes designated as an "endocrine" cytokine because of its strong regulatory influence on hormone production. Systemically acting IL-6 derived from immune cells is a potent stimulator of the hypothalamus-pituitary-adrenal axis and therefore plays an important role in modulating immune-neuroendocrine interactions during inflammatory or infectious processes. However, IL-6 is also produced within the anterior pituitary by so-called folliculostellate (FS) cells and is also synthesized in and released by tumor cells in pituitary adenomas. Growth factors (e.g., transforming growth factor-beta), neuropeptides (e.g., pituitary adenylate cyclase-activating polypeptide), or hormones (e.g., glucocorticoids) regulate IL-6 production both in FS and pituitary tumor cells. Interestingly, components of the innate immune system, such as toll-like receptor 4 and nucleotide-binding oligomerization domains (NODs), are expressed in FS and pituitary tumor cells. Therefore, cell-wall components of bacteria (lipopolysaccharide, muramyl dipeptide, diamino pimelic acid) stimulate IL-6 production in normal and tumoral pituitary. The intrinsic IL-6 production by FS cells in normal anterior pituitary may participate in immune-neuroendocrine interactions during inflammatory processes. In pituitary adenomas, IL-6 stimulates hormone secretion, tumor cell proliferation, and the production of angiogenic factors, such as vascular endothelial growth factor-A, suggesting an important role of IL-6 in the pathophysiology and progression of pituitary adenomas.

The characteristic change in the distribution of S-100 immunoreactive folliculostellate cells in rat anterior pituitary upon long-term estrogen treatment is prevented by concomitant progesterone treatment

The presence of folliculostellate cells in the anterior pituitary was described 49 years ago. These cells give about 10% of the whole cell population and through their long processes they provide intrahypophyseal communication. The folliculostellate cells contain S-100 protein. Its immunostaining was used to identify these cells. It was previously found that the diethylstilbestrol treatment basically influences the morphology and function of the trophic hormone secreting as well as the folliculostellate cells. In the present experiment, we have studied whether a concomitant progesterone treatment can prevent or attenuate changes caused by diethylstilbestrol treatment in the distribution of folliculostellate, prolactin, and GH cells. Diethylstilbestrol alone induced the appearance of prolactinomas. Inside the prolactinomas, folliculostellate cells were scattered but outside the prolactinomas they formed a demarcation line. Inside the prolactinomas, there were only a few growth hormone immunoreactive cells but they surrounded the prolactinomas in a ring-like pattern. When diethylstilbestrol was implanted with progesterone, the changes being characteristic for diethylstilbestrol treatment, could not develop. Concomitant progesterone influence prevented morphological changes in the anterior pituitary. Progesterone alone had no effect. In accordance with the formation of prolactinomas, the plasma prolactin level was very high in diethylstilbestrol treated rats. Concomitant progesterone treatment prevented the effect of diethylstilbestrol. Progesterone alone did not influence the prolactin level. GH levels did not significantly differ in any groups.

Pituitary adenoma with rich folliculo-stellate cells and mucin-producing epithelia arising in a 2-year-old girl

Pituitary adenoma is a rare neoplasm in childhood, with prolactin and adrenocorticotropic hormone (ACTH)-secreting adenomas predominating in this age group. Herein is reported a case of an ACTH-producing macroadenoma with an unusual histology that occurred in a 2-year-old girl. Because of the patient's age and the macroadenoma's suprasellar location and large size (up to 4 cm in diameter), radical surgery was performed under the suspicion of craniopharyngioma or germ-cell tumor. Pathologically, it was a unique pituitary adenoma composed of monotonous ACTH-producing cells, smaller folliculo-stellate cells (FSC), and mucin-producing cells. The FSC, non-hormone-secreting pituitary cells of uncertain function, were confirmed by their S-100 protein, glial fibrillary acidic protein and cytokeratin expression immunoprofiles. The abrupt transition between the prominent gland-forming mucin-producing epithelia and the FSC component suggested that the mucin-producing epithelia might be derived from the FSC. This association might represent so-called 'retrodifferentiation' of adenoma cells to the FSC and the precursor cells of Rathke's pouch.

Diversity of ACTH-immunoreactive cells in the human adenohypophysis: an immunohistochemical study with special reference to cluster formation and follicular cell association

Horvath et al. called relatively small ACTH-immunoreactive (ACTH-IR) cells observed in basophil invasion "proopiomelanocortin (POMC) cells," and these cells were supposed to be different from larger ACTH-IR cells in human adenohypophysis. To clarify the existence of "anterior POMC cells," we examined 21 autopsy cases taking note of follicular cells (FCs). We found that smaller ACTH-IR cells were clustered forming small areas without FC association, clustered small cell island (CSCI). CSCI was found in all the specimens we examined using immunohistochemical staining for ACTH and cytokeratin (AE1/AE3) in serial sections. ACTH-IR cells outside CSCI were of various sizes, mainly consisting of larger ACTH-IR cells that were diffusely scattered among other hormone-secreting cells and closely associated with FCs. By immunohistochemistry, ACTH-IR cells within CSCI and basophil invasion showed uniformly weak reactivity and common patterns for cytokeratins (CAM5.2 and 35 beta H11), carboxypeptidase D, and LeuM1, whereas those outside CSCI showed a great variety of immunoreactivity. The similarity in the immunoreactivity of ACTH-IR cells between CSCI and basophil invasion suggests that ACTH-IR cells in these two areas have common characteristics and ACTH-IR cells in CSCI are most likely "POMC cells." The clustered "anterior POMC cells" may be distinguishable by light microscopic immunohistochemistry.