Useful diagnostic histogenetic features of ectopic odontogenic ghost cell tumours.

BACKGROUND: Ectopic odontogenic tumours are rare and difficult to diagnose. Consequently, they are occasionally misdiagnosed as other tumours and overtreated. Dentinogenic ghost cell tumours (DGCTs) are odontogenic neoplasms characterised by a CTNNB1 mutation, ghost cell appearance, and dentinoid-like calcification. Herein, we present a case of ectopic DGCT on the floor of a patient's mouth, providing reliable clinicopathological and genetic evidence of its odontogenicity for the first time. CASE PRESENTATION: A 72-year-old man presented with painless sublingual swelling. Imaging revealed a multi-lobulated, solid-cystic mass on the floor of his mouth. Cytological evaluation showed folded epithelial clusters composed of basaloid cells, keratinised material, and calcification. Histological analysis revealed a multi-cystic, cribriform to solid nest, with an odontogenic satellate reticulum-like epithelium, including ghost cells and dentinoid matrix deposition. Immunohistochemical analysis found that CK19, CK5/6, bcl-2, and p63 were diffuse positive, ß-catenin was focal positive in the nuclei, and the cells in the dentinoid matrix were positive for DMP1. The CTNTTB1 mutation was detected, leading to the final diagnosis of ectopic DGCT. There was no recurrence during the 6-month follow-up. CONCLUSIONS: Overall, we have presented a comprehensive clinical overview of DGCT and identified its pathological and genetic features. This report will aid in the recognition of this rare disease in the future and help to avoid misdiagnosis and overtreatment.

Fine-needle aspiration cytology of Warthin-like mucoepidermoid carcinoma: A case report with cytological review.

Warthin-like mucoepidermoid carcinoma (MEC) is a novel and rare subtype of MEC and is characterized histopathologically by the presence of abundant lymphocytic infiltration and cystic changes. A small number of cytological reports of this MEC variant is currently available. The present study reported on the sixth cytological case of Warthin-like MEC, reviewed the cytological features of the tumour and discussed the cytological differential diagnosis. A 16-year-old Japanese female presented with a painful mass in the left parotid gland. Fine-needle aspiration for cytological examination of the parotid gland tumour was performed, followed by partial parotidectomy. Cytological examination revealed sheet-like and folded epithelial cell clusters in a mucinous background accompanying abundant lymphocytic infiltration. Epithelial clusters comprised round cells with mildly enlarged round to oval nuclei, polygonal cells with relatively rich cytoplasm and slightly enlarged round to oval nuclei. Certain polygonal cells contained intracytoplasmic mucin. Histopathological examination of the resected parotid gland tumour indicated multiple cystic lesions with abundant lymphocytic infiltration accompanying lymphoid follicle formation. The cysts were lined by intermediate cells with occasional mucinous cells. Fluorescence in situ hybridization using the surgically resected specimen indicated mastermind-like transcriptional coactivator 2 (MAML2) rearrangement, a characteristic of Warthin-like MEC. Consequently, the patient was diagnosed with Warthin-like MEC. The literature review revealed that the characteristic cytological features of Warthin-like MEC are the presence of intermediate cells and lack of oncocytic cells in the mucinous material under an abundant lymphocytic background. Clinicopathological features may help with a differential diagnosis, particularly from Warthin's tumour, and detection of MAML2 rearrangement is able to improve the accuracy of diagnosis.

Clinicopathological characteristics of pancreatic ductal adenocarcinoma with invasive micropapillary carcinoma component with emphasis on the usefulness of PKCζ immunostaining for detection of reverse polarity.

Invasive micropapillary carcinoma (IMPC) is a rare distinct histopathological subtype, characterized by the presence of carcinoma cells displaying reverse polarity. Only limited clinicopathological information is available regarding pancreatic IMPC. The aim of the present study was to clarify the clinicopathological features of pancreatic IMPC and the usefulness of protein kinase C (PKC)ζ immunostaining for the detection of reverse polarity. We reviewed 242 consecutive surgically resected specimens of pancreatic ductal adenocarcinoma and selected samples with an IMPC component. Clinicopathological characteristics were compared between the IMPC and non-IMPC groups. Immunohistochemical staining for PKCζ was performed using an autostainer. In total, 14 cases had an IMPC component (5.8%). The extent of IMPC component ranged from 5 to 20%. There were no significant differences in tumor location, T category, lymph node metastatic status, preoperative carbohydrate antigen 19-9 level, resection status and overall survival between the IMPC and non-IMPC groups. Immunostaining for PKCζ clearly showed reverse polarity of the neoplastic cells of IMPC. Although previous reports have shown that the presence of an IMPC component (>20% of the tumor) indicated poor prognosis, the present study demonstrated that presence of IMPC <20% did not suggest a worse prognosis.

Utility of an immunocytochemical analysis for pan-Trk in the cytodiagnosis of secretory carcinoma of the salivary gland.

Secretory carcinoma (SC) of the salivary gland is a rare distinct clinicopathological entity characterized by the presence of the ETV6-NTRK3 fusion. Although the characteristic cytological features of SC have been recognized, its cytodiagnosis, especially differentiating SC from acinic cell carcinoma, is challenging. Recent studies have revealed that immunohistochemistry for pan-tyrosine receptor kinase (Trk) and nuclear receptor subfamily 4 group member 3 (NR4A3) are specific for SC and acinic cell carcinoma, respectively. However, the usefulness of immunocytochemical detection of these markers in the diagnosis of SC has not been addressed. Hence, the present study aimed to analyze the usefulness of immunocytochemical staining for pan-Trk and NR4A3 in the cytodiagnosis of SC. We enrolled eight patients with a histopathological diagnosis of SC who underwent preoperative fine-needle aspiration cytological examination. The cytological characteristics were reviewed and immunocytochemical staining for pan-Trk and NR4A3 was performed. The characteristic cytological features noted in the patient cohort included neoplastic cell clusters with a sheet-like and papillary cluster arrangement as well as single cells. Additionally, neoplastic cells with mild to moderately enlarged nuclei and small nucleoli, multi-vacuolated cytoplasm, and intracytoplasmic mucin were also observed. The immunocytochemical analyses clearly demonstrated that all eight specimens showed positive nuclear staining for pan-Trk, but were negative for NR4A3 expression. Although all cases of SC do not always show positive immunoreactivity for pan-Trk, immunocytochemical analysis for pan-Trk may be useful for the cytodiagnosis of SC along with assessment of the characteristic cytological features.

Spontaneous infarction of pleomorphic adenoma of the parotid gland: A case report.

Infarction after the fine-needle aspiration (FNA) procedure is a well-recognized phenomenon of salivary gland lesions. Though extremely rare, spontaneous infarction without previous FNA can occur in pleomorphic adenoma (PA). The present report describes a fourth cytological case of spontaneous infarction of PA of the parotid gland using immunocytochemical analysis, to the best of our knowledge, for the first time. A 57-year-old Japanese female presented with persistent swelling of the right neck region. Physical examination revealed a tumour in the right parotid gland, and FNA examination of the tumour was performed following surgical resection. The Papanicolaou smear demonstrated the presence of fully necrotic cell clusters of varying sizes in a necrotic background. Only a few viable cell clusters were observed. These cells were polygonal to spindle-shaped, and exhibited large round to oval nuclei with a conspicuous nucleoli. Although nuclear pleomorphism was noted, the nuclear chromatin was fine. No neoplastic myoepithelial cells were observed. Therefore, it was suspected that these cells were malignant. Immunocytochemical analysis indicated that these atypical cells were positive for p40. Histopathological examination of the resected parotid gland tumour revealed infarcted PA. Our study revealed that the presence of atypical squamous metaplastic cells in a necrotic background was a characteristic cytological feature of infarcted PA, and that these atypical squamous cells can have large nuclei with conspicuous nucleoli and exhibit pleomorphism. Although cytological diagnosis of infarcted PA is difficult, pathologists and cytopathologists must consider the presence of atypical metaplastic squamous cells in benign salivary gland tumours, including infarcted PA.

Immunohistochemical analysis of SOX2 expression in small-cell neuroendocrine carcinoma of the endometrium.

Small-cell neuroendocrine carcinoma (NEC) of the endometrium is an extremely rare and highly aggressive carcinoma. Sex-determining region Y-box 2 (SOX2) is a master transcription factor regulating the self-renewal, maintenance of stem cell properties and pluripotency of embryonic stem cells, and recent studies revealed that SOX2 plays important roles in cancer growth and progression in several types of carcinomas, including small-cell neuroendocrine carcinoma (NEC) of the lung and oesophagus. Few studies to date have analysed the association between SOX2 and endometrioid carcinoma, whereas the expression of SOX2 in small-cell NEC of the endometrium has not been investigated. The aim of the present study was to analyse the expression status of SOX2, p16 and paired-box gene (PAX) 8, a useful Müllerian marker, in endometrial small-cell NEC. A total of 4 patients with small-cell NEC of the endometrium were enrolled (median age, 70 years). Immunohistochemical studies revealed SOX2 expression in 3 patients and p16 expression in all patients. No patients exhibited positive immunoreactivity for PAX8. SOX2 expression has been reported to be associated with the pathogenesis of small-cell NEC of the oesophagus. Therefore, the results of the present study indicated that SOX2 expression plays an important role in the development of small-cell NEC of the endometrium and the oesophagus. Moreover, expression of p16 and loss of PAX8 do not indicate the origin of small-cell NEC of the endometrium.

Small-cell neuroendocrine carcinoma in directly sampled endometrial cytology: A monocentric retrospective study of six cases.

Small-cell neuroendocrine carcinoma (NEC) of the endometrium is extremely rare, and demonstrates an aggressive clinical course. Since reports describing its cytological features are scarce, we aimed to retrospectively analyze these features. Patients with a histopathological diagnosis of NEC who underwent preoperative cytological examination, were enrolled in this study. The cytological features including the background, arrangement, and shape of the neoplastic cells, and the nuclear and cytoplasmic features were reviewed; six patients were enrolled. The conventionally stained, directly sampled cytological specimens showed small neoplastic cell clusters in all cases, as well as isolated neoplastic cells and large clusters in 3 and 2 cases, respectively, in inflammatory or necrotic backgrounds. These neoplastic cells had a high nuclear/cytoplasmic ratio, and round to oval nuclei with powdery chromatin, inconspicuous nucleoli, and scant cytoplasm. Nuclear molding was a characteristic finding. An adenocarcinoma component was also present in 3 cases. Initial cytodiagnosis revealed small-cell NEC and adenocarcinoma or suspected adenocarcinoma in 1 and 4 cases, respectively. The one remaining case was found to be negative and was considered as degenerated endometrial stromal cells. Primarily owing to overlooking this component, the initial cytodiagnostic accuracy of small-cell NEC was low, particularly in cases with coexisting adenocarcinoma. However, the cytological features of this tumor were characteristic. Therefore, although extremely rare, careful observation is essential for an early and accurate diagnosis and to prevent overlooking the small-cell NEC component.

Cytological features of basal cell adenocarcinoma of the salivary glands.

The cytological features of basal cell adenocarcinoma (BAC) of the salivary gland, a rare carcinoma, have not been well described. This study included patients who were histopathologically diagnosed with BAC and who underwent preoperative fine-needle aspiration cytological examination. Cytological characteristics, including background, arrangement and shape of the neoplastic cells, nuclear and cytoplasmic features, and presence of stromal spindle cells, were reviewed. Seven patients were enrolled in the study. The cytological specimens were cellular and composed of large or small clusters with occasional discohesive neoplastic cells at the periphery. The predominant cellular morphology was spindle-shaped in four cases, and small round-shaped in three cases. These neoplastic cells were tightly packed, showed high cellularity and overlapping nuclei, and had mildly to moderately enlarged round to oval nuclei with occasional small nucleoli and scant cytoplasm. Stromal spindle cells were observed around the basaloid cells in three cases (42.9%). All histology-proven stromal spindle cell-positive cases had stromal spindle cells in the cytological specimens. The study findings clearly demonstrate the relatively high frequency of stromal spindle cells in cytological specimens of BAC. This finding is characteristic of BAC, although basal cell adenoma of salivary gland frequently has stromal spindle cells in the cytological specimens. The characteristic that differentiates BAC from basal cell adenoma is the presence of tightly packed and high cellular clusters with discohesive neoplastic cells. An understanding of these cytological features can aid the cytodiagnosis of BAC.

Cytological features of basal cell adenoma of salivary glands: Analysis of 19 cases emphasizing stromal spindle cells.

BACKGROUND: Basal cell adenoma (BCA) of the salivary gland is a relatively rare benign tumor. Although the presence of stromal spindle cells is a characteristic histopathological feature, this finding has not been the focus of much attention in the cytodiagnosis of BCA. Thus, we analyzed the cytological features of BCA, especially the presence of stromal spindle cells. METHODS: Patients who were histopathologically diagnosed with BCA and underwent preoperative fine-needle aspiration cytological examination were enrolled in this study. The cytological characteristics including arrangement and shape of the neoplastic cells, nuclear and cytoplasmic features, and the presence of stromal spindle cells were reviewed. RESULTS: Nineteen patients were enrolled in the study. The cytological specimens were cellular and composed of small or large clusters or both. The neoplastic cells had scant cytoplasm and small round to oval nuclei. Basement membrane-like material was observed in 57.9%, and peripheral palisading was noted in 84.2%. Loose aggregates of stromal spindle cells were present in 63.2%, and the stromal spindle cells shown in the histological examination of 85.7% of cases were expressed in the cytological specimens. CONCLUSION: This study clearly demonstrated the relatively high frequency of stromal spindle cells in cytological specimens of BCA. This finding is characteristic of BCA, and therefore, the combination of cytological features, including packed clusters of neoplastic cells with scant cytoplasm and small nuclei, peripheral palisading, and basement membrane-like material, and the presence of stromal spindle cells could increase the diagnostic success of BCA.

Metastatic salivary duct carcinoma in cardiac and pleural effusions: A case report with immunocytochemical analysis for androgen receptor and HER2.

Salivary duct carcinoma (SDC) is a relatively rare highly aggressive salivary gland tumor. Although SDC shows frequent lymph node and distant metastases, the presence of neoplastic cells in the pleural effusion is extremely rare. In this report, we describe the first documented cytological case of metastatic SDC in cardiac and pleural effusions with immunocytochemical analyses for androgen receptor (AR) and human epidermal growth factor receptor (HER)2. A 52-year-old Japanese male developed cardiac tamponade and respiratory discomfort after surgery and chemo-radiation therapy for SDC of the right submandibular gland. Aspiration of the cardiac and pleural effusions was performed. The Papanicolaou-stained cytological specimens of cardiac and pleural effusions showed that numerous small ball-like or papillary structures were present in an inflammatory background. The neoplastic cells had rich granular cytoplasm and large round to oval nuclei containing conspicuous nucleoli. Immunocytochemical analyses clearly demonstrated positivity for AR and strong membranous expression of HER2 in the neoplastic cells. Accordingly, a cytodiagnosis of metastatic SDC was made. Recently, HER2-targeted or AR deprivation therapy have been introduced for patients with SDC, therefore, determination of expression profiles of AR and HER2 may be crucial for developing a treatment strategy for patients with metastatic SDC. According to the results of the present report, immunocytochemical analyses for AR and HER2 in the effusion specimens may be useful for determination of a treatment strategy for patients with metastatic SDC.

Imprint cytology of strumal carcinoid of the ovary: A case report with immunocytochemical analysis.

Strumal carcinoid is a rare ovarian tumor defined as carcinoid associated with struma ovarii. We report here the second cytological case of strumal carcinoid and performed immunocytochemical analysis for the first time. A 68-year-old Japanese female was found to have a solid tumor with small cystic components in the left ovary, and bilateral salpingo-oophorectomy was performed. The Papanicolaou smear of the imprint cytological specimen of the left ovarian tumor revealed presence of two distinct components. The first component included thyroid follicles, which was composed of flat sheets of polygonal epithelial cells without nuclear groove and intranuclear inclusion. The other component was composed of trabecular clusters of columnar cells containing round to slender nuclei with "salt and pepper" chromatin. Immunocytochemical analysis revealed that synaptophysin was expressed in the latter component. Therefore, a cytodiagnosis of strumal carcinoid was made. Histopathological analyses confirmed the diagnosis of strumal carcinoid. Albeit rare, carcinoid tumor occurs in the ovary, and the recognition of characteristic nuclear features and cellular arrangement leads to correct cytodiagnosis. Presence of struma ovarii component suggests an ovarian origin. Moreover, immunocytochemical analysis for neuroendocrine markers aids its differential diagnosis from granulosa cell tumor and carcinoma arising from struma ovarii.

Cytological characteristics of meningeal solitary fibrous tumor metastatic to the lung: A case report with immunocytochemical analysis.

Solitary fibrous tumor (SFT) is a relatively uncommon mesenchymal tumor, and its occurrence in the meninges is rare. We herein report what is, to the best of our knowledge, the first cytological case of meningeal SFT metastatic to the lung with immunocytochemical analysis for signal transducer and activator of transcription 6 (STAT6), and compare the cytological characteristics to those of pleuropulmonary SFT. A 58-year-old Japanese male patient was found to have multiple nodules in the bilateral lungs after surgery for meningeal SFT. Partial resection of the nodules was performed, and touch smears were obtained. The Papanicolaou smear revealed cohesive hypercellular clusters of polygonal to elongated neoplastic cells with scant cytoplasm and oval to short spindle-shaped nuclei with nucleoli containing coarse chromatin. Mild-to-moderate nuclear pleomorphism was observed. No collagenous stroma was noted. Immunocytochemical analysis revealed that the neoplastic cells diffusely expressed STAT6. Histopathological and immunohistochemical studies confirmed the diagnosis of meningeal SFT metastatic to the lung. Moreover, reverse transcription-polymerase chain reaction analysis revealed that the lung tumor harbored NAB2ex6-STAT6ex16 fusion. Recent studies demonstrated that there is a clinicopathological difference among NAB2-STAT6 fusion variants in SFT. As reflected in fusion variants, meningeal SFT occasionally lacks collagenous stroma, as in the present case, although the most characteristic cytological feature of SFT is the presence of spindle-shaped neoplastic cells embedded in dense collagenous stroma. Thus, immunocytochemical analysis for STAT6 is very useful for diagnosing SFT.

Cytological features of hepatoid adenocarcinoma of the gallbladder: A case report with immunocytochemical analyzes.

Hepatoid adenocarcinoma is defined as an extrahepatic malignant neoplasm showing morphological and immunohistochemical resemblance of hepatocellular carcinoma. The occurrence of this type of tumor in the gallbladder is extremely rare. In this study, we report the first cytological case of hepatoid adenocarcinoma of the gallbladder. An 80-year-old Japanese female was found to have a tumorous lesion in the gallbladder. Papanicolaou smear of the ascites demonstrated a few epithelial cell clusters composed of round to oval neoplastic cells with distinct cell border and large centrally-located nuclei. Tumor touch smear of the resected tumor revealed the presence of two distinct neoplastic components. The first component was composed of clusters or sheets of epithelial cells with distinct cell border, relatively rich clear cytoplasm, and centrally-located nuclei, as seen in the ascites specimen. The other component was composed of tall columnar cells with large basally-oriented nuclei, and glandular formation was noted as well. Immunocytochemical analyzes of the touch smear material demonstrated that the former component was positive for HepPar1, thus it was considered as a hepatoid adenocarcinoma, and the latter component deemed as a typical adenocarcinoma. Histopathological and immunohistochemical examination of the resected gallbladder tumor confirmed a diagnosis of hepatoid adenocarcinoma. The characteristic cytological features of hepatoid adenocarcinoma are the presence of sheets or clusters of neoplastic cells with distinct cell border and centrally-located nuclei. Immunocytochemical analysis for HepPar1 may help its diagnosis. Demonstration of hepatoid adenocarcinoma is important in the cytological specimen because this type of tumor shows an aggressive clinical course.

Combined small cell carcinoma with giant cell carcinoma component of the lung: A case successfully diagnosed by computed tomography-guided fine-needle aspiration cytology.

Combined small cell lung carcinoma (SCLC) is a rare variant of SCLC and is defined as a mixture of SCLC and non-SCLC components. Although any histopathological subtype may be present as a non-SCLC component, the presence of pleomorphic carcinoma components are extremely rare. The present report describes the first documented cytological features of combined SCLC with a giant cell carcinoma component. A 50-year-old Japanese female with a history of smoking presented with a mass lesion in the left lung. Computed tomography-guided fine-needle aspiration cytology and needle biopsy were performed, followed by a lobectomy. A Papanicolaou smear revealed the presence of two distinct neoplastic components in a necrotic background. One component was SCLC, which comprised small-sized neoplastic cells containing scant cytoplasm and round to oval nuclei with dispersed granular chromatin without nucleoli. The other component was giant cell carcinoma, which was composed of large-sized neoplastic cells containing irregular large hyperchromatic nuclei (approximately 7 to 10 times larger than those of SCLC). SCLC was demonstrated in the biopsy specimen, however no giant cell carcinoma component was present. Histopathological study of the lobectomy specimen verified a diagnosis of combined SCLC with giant cell carcinoma component. Both SCLC and giant cell carcinoma exhibit characteristic cytological features, therefore, albeit extremely rare, careful observation may lead to a correct diagnosis of combined SCLC in the cytological specimen.

Cytological features of mixed adenoneuroendocrine carcinoma of the ampulla of Vater: A case report with immunocytochemical analyses.

Mixed adenoneuroendocrine carcinoma (MANEC) is defined as a tumor that has morphologically recognizable both adenocarcinoma and neuroendocrine carcinoma components comprising at least 30% of either components. MANEC occurring in the ampulla of Vater is extremely rare, and only 16 cases have been reported in the English language literature. In the present report, we describe the first case of MANEC of the ampulla of Vater with immunocytochemical analyses. An 82-year-old Japanese male was incidentally found to have a tumorous lesion in the ampulla of Vater. Endoscopic ultrasound-fine needle aspiration (EUS-FNA) of the tumor was performed. The Papanicolaou smear demonstrated the presence of different three components. The most dominant component was cohesive clusters of small round cells with round to oval nuclei with powdery chromatin and scant cytoplasm, which corresponded to small cell carcinoma. The second component was an adenocarcinoma, which was composed of irregularly overlapping clusters of tall columnar cells with large round to oval nuclei containing conspicuous nucleoli. The third component was an adenoma, which was comprised of flat cohesive clusters of columnar cells without atypia. Immunocytochemical analyses demonstrated that synaptophysin was expressed in the small round cells, and cdx-2 was expressed in all three components. Accordingly, a cytodiagnosis of MANEC with adenoma component was made. Preoperative diagnosis of ampullary MANEC is difficult. However, this report clearly demonstrates three different components in the EUS-FNA cytological specimen. Therefore, we suggest that cytological examination is a useful method for diagnosis of MANEC of the ampulla of Vater.

Thymic enteric type adenocarcinoma: A case report with cytological features.

Primary thymic adenocarcinoma is an extremely rare tumor, and thymic enteric type adenocarcinoma has recently been proposed as a distinct pathological entity. Herein, we report the first cytological description of thymic enteric type adenocarcinoma. A 29-year-old Japanese female without a significant past medical history was found to have an abnormal chest shadow. Chest computed tomography demonstrated a well-circumscribed tumor in the anterior mediastinum, and thymectomy was performed. The Papanicolaou staining of the touch smear of the resected tumor demonstrated tightly cohesive epithelial cell clusters in a necrotic background. These cells were cuboidal to columnar in shape and had large round to oval nuclei with conspicuous nucleoli. Some of these neoplastic cells had intracytoplasmic mucin. Immunocytochemically, the neoplastic cells were positive for cytokeratin 20 and CDX-2. Histopathological study revealed tubular and papillotubular neoplastic growth composed of cuboidal to columnar neoplastic cells that contained large round to oval nuclei. Some of the neoplastic cells had intracytoplasmic mucin. Immunohistochemical study confirmed the expression of cytokeratin 20 and CDX-2. The final diagnosis of thymic enteric type adenocarcinoma was made. The cytological and immunocytochemical features of this case led to a diagnosis of enteric type adenocarcinoma. However, these features alone cannot be differentiated from a metastatic adenocarcinoma arising from the gastrointestinal tract. Cytological examination of a fine-needle aspiration of the mediastinal tumor has been reported to be useful in making a diagnosis. Therefore, an awareness of this new pathological entity is important for differentiating a thymic tumor from a metastatic carcinoma in the thymus.

Cytological features of atypical polypoid adenomyoma of the endometrium: A case report with literature review.

Atypical polypoid adenomyoma (APA) is a rare mixed epithelial and mesenchymal tumor characterized histopathologically by the presence of disorganized hyperplastic glands with cytological atypia embedded in intersecting fascicles of fibromuscular stromal cells. Herein, we report the first documented endometrial cytological case of APA. A 35-year-old Japanese female presented with irregular menstrual cycles and then was found to have polypoid lesions of the endometrium. Cytological examination of the endometrium and endometrial curettage were performed. The Papanicolaou smear revealed the presence of abundant clusters of crowded glandular cells in a clean background. These clusters exhibited irregular branching and dilatation, and these glandular cells had mild to moderately enlarged round to oval nuclei. Within the dilated glands, metaplastic squamous cells (squamous morules) were observed. The most striking feature was the presence of short fascicles of the spindle cells without atypia around the dilated atypical glandular cell clusters with squamous morules. Histopathological and immunohistochemical examinations revealed a diagnosis of APA. Our report demonstrates that the characteristic cytological feature suggestive of APA is the presence of short fascicles of the spindle cells without atypia surrounding dilated atypical glandular cell clusters with squamous morules in a clean background, and their appearance can allow cytologists/cytopathologists to consider APA in differential diagnosis in the endometrial cytological specimens. Diagn. Cytopathol. 2017;45:345-349. © 2016 Wiley Periodicals, Inc.