Cytologic diagnosis of thyroid‐like follicular carcinoma of the kidney: A case report

Thyroid‐like follicular carcinoma of the kidney (TLFCK) is a recently described subtype of renal‐cell carcinoma that is not currently included in the World Health Organization classification. Few sporadic case reports and one series have been reported with emphasis on histopathologic features. However, cytological features have not been described in the literature to date. A 34‐year‐old male presented with a renal mass. An intraoperative smear preparation of the tumor revealed a hypercellular smear with cells arranged in sheets without any follicular, papillary, or acinar arrangement. The most striking feature was the presence of acellular eosinophilic material associated with the neoplastic epithelial cells in the background of the smear. Individual tumor cells were oval, round, and plasmacytoid with mild nuclear pleomorphism, finely stippled nuclear chromatin, and inconspicuous nucleoli with moderate amount of eosinophilic cytoplasm and rare nuclear grooves. It was unclear at the time of the intraoperative assessment of the smear if the acellular eosinophilic material represented metachromatic matrix‐like extracellular material, mucin, colloid, amyloid, or hyaline material. The differential diagnoses included a primary renal‐cell carcinoma versus a metastatic tumor. Subsequent histopathologic examination was diagnostic of a rare, recently described primary neoplasm of the kidney called TLFCK. This work is a retrospective evaluation of the cytological features of TLFCK. It is important for cytopathologists to be aware of this entity and its cytological features to render a correct diagnosis for adequate management of these patients. Diagn. Cytopathol. 2014;42:273–277. © 2012 Wiley Periodicals, Inc.     

Clear‐cell hidradenoma in a child: A diagnostic dilemma for the cytopathologist

Primary cutaneous tumors are infrequently subjected to fine needle aspiration cytology. As a result, the cytological reports of skin adnexal tumors like hidradenoma are scarce in the available literature. A young boy with a painless nodule on forehead underwent fine needle aspiration. The smears showed clusters of epithelial cells containing blue cytoplasm, some of which had vacuolated cytoplasm with mild nuclear pleomorphism and occasional larger hyperchromatic nucleus. The cytological features, in conjunction with the clinical examination, suggested a skin appendageal tumor. Though nuclear pleomorphism and occasional larger nucleus posed a cytological diagnostic challenge, a diagnosis of benign appendageal tumor was suggested, considering the young age of the patient. This was later confirmed as a clear‐cell hidradenoma on excision biopsy. The cytopathologist should consider skin appendageal tumors during evaluation of cutaneous nodules. An accurate diagnosis requires a close clinico‐pathologic correlation. Diagn. Cytopathol. 2009. © 2009 Wiley‐Liss, Inc.     

Cytopathology of high‐grade papillary thyroid carcinomas: Tall‐cell variant,diffuse sclerosing variant,and poorly differentiated papillary carcinoma

Cytologic reports of the aggressive tall‐cell and diffuse sclerosing variants of papillary carcinoma have emphasized features such as tall and large cells, increased nuclear size, nuclear pleomorphism, intranuclear pseudoinclusions, three‐dimensional tissue fragments, squamous‐like cells, and dense inflammatory background as characteristic features. However, the specificity of these features in identifying the particular variants and distinguishing them from other poorly differentiated papillary carcinomas and typical low‐grade forms of papillary carcinoma has not been established. The objective of this study was to assess the predictive value of these reported cytologic features. Fourteen cases of high‐grade papillary carcinoma consisting of the aggressive variants (tall‐cell variant (tcv) and diffuse sclerosing variant (dsv)) and poorly differentiated papillary carcinomas (pdpc) were compared to 18 cases of low‐grade papillary carcinoma. Seven cytologic features consisting of the presence of tall and large cells, architectural disorganization, nuclear enlargement, prominent intranuclear pseudoinclusions, nuclear pleomorphism, lymphocytic infiltrate, and squamoid appearance of the neoplastic cells were evaluated. Cytology samples from tcv, dsv, and pdpc consistently demonstrated 3 of the 7 cytologic features (architectural disorganization, nuclear enlargement, and pleomorphism). In contrast, only two of the samples from low‐grade cases demonstrated these 3 features. The recognition of these 3 cytologic features had a positive predictive value of 88% and a negative predictive value of 100% for identifying tcv, dsv, and pdpc. The remaining cytologic features were not a consistent feature in the variants, and by cytology alone, distinction between the aggressive variants (dsv and tcv) and pdpc could not be made. Diagn. Cytopathol. 1999;20:19–23. © 1999 Wiley‐Liss, Inc.     

Fine‐needle aspiration cytology of triple‐negative basal‐like breast cancer

Invasive breast cancer is divided into luminal A, luminal B, HER2 overexpression, basal‐like (BL) and normal‐like subtypes, among which the BL subtype has the worst prognosis. The purpose of this study was to determine the clinicopathological and cytological characteristics of BL breast cancer (BLBC). Fine‐needle aspiration cytology samples from 17 patients with consecutive BLBC were investigated, and the findings were compared with those of other subtypes (10 cases each) for the following cytomorphological features: necrosis; lymphocyte infiltration; mitotic index; apoptosis; naked nuclei; nuclear/cytoplasmic ratio; nuclear margin, size and pleomorphism; chromatin granularity and density; and nucleolar appearance. Histologically, the BLBCs were heterogeneous, and included medullary carcinoma and metaplastic carcinoma, in addition to invasive ductal carcinoma. Cytologically, high mitotic index, naked nuclei, and irregular nuclear margin were significantly observed when compared with both the luminal A and B subtypes. Large nuclei with nucleoli and lymphocyte infiltration were frequently seen compared with the luminal A and B subtypes, respectively. Squamous nodules were seen in all metaplastic cases, but not in the HER2 overexpression subtype. Lymphocyte infiltration, squamous metaplasia, and nuclear findings such as a high mitotic index, naked or large nuclei, an irregular nuclear margin and the presence of nucleoli, may be clues indicating BLBC. Diagn. Cytopathol. 2013;41:283–287. © 2011 Wiley Periodicals, Inc.     

Cytology of a sarcomatoid renal cell carcinoma with unusual coexpression of S‐100 protein: A case report,review of the literature and cytologic–histologic correlation

Sarcomatoid renal cell carcinoma (SRCC) is an aggressive variant of renal cell carcinoma; it is an uncommon, malignant neoplasm, and its diagnosis is usually based on the histologic evaluation of a nephrectomy specimen. Patients are treated with systemic therapy and, generally, a nephrectomy is not performed. Therefore, arriving at an accurate diagnosis is critical for planning further management. Cytomorphological findings of SRCC have rarely been reported. This article reports the cytological findings in a case of SRCC composed predominantly of spindle cells and discusses its differential diagnosis in a 50‐year‐old female who presented with sharp right groin pain. A CT scan showed an enlargement of the right kidney. Cytology smears showed a malignant neoplasm composed predominantly of spindle cells. A panel of immunohistochemical stains performed on a core biopsy confirmed the epithelial nature of the spindle cells. A diffuse positive staining of the neoplastic cells for S‐100 protein was also observed. It has been reported in the medical literature that almost all SRCC cases demonstrate negative staining for S‐100 protein, with only a single case having been reported as focally positive. The cytologic differential diagnosis of spindle cell neoplasm with expression of S‐100 protein should be broadened to include SRCC. Furthermore, the S‐100 protein expression in SRCC that was observed in this case merits further investigation. Diagn. Cytopathol. 2009. © 2008 Wiley‐Liss, Inc.     

Parathyroid fine‐needle aspiration cytology in the evaluation of parathyroid adenoma: Cytologic findings from 53 patients

This study was designed to assess the utility of fine‐needle aspiration cytology (FNAC) in the preoperative localization of parathyroid adenoma (PA). Fifty‐seven samples from fifty‐three cases of PA (four patients had bilateral disease) were obtained by ultrasound (US)‐guided fine‐needle aspiration. Parathyroid hormone (PTH) estimation was performed on the supernatant of the aspirated fluid on all cases. Subsequently, all of them underwent cytologic evaluation. The cytology slides were evaluated using the following criteria: Cellularity, architectural patterns, bare nuclei in the background, nuclear morphology, and background features (colloid‐like material or macrophages). Parathyroid cells were seen in 23 samples (40.4%). The cellularity of the smears was insufficient for interpretation in 16 samples (28.1%); and thyroid follicles and colloid were seen in 18 samples (31.5%). Majority of the samples with parathyroid cells showed moderate cellularity with monomorphous round to slightly oval cells predominantly arranged in loose two‐dimensional clusters with occasional papillary fragments. Majority of them exhibited a stippled nuclear chromatin. No significant pleomorphism, mitotic activity, or prominent nucleoli were observed. Most samples showed bare nuclei in the background. In conclusion, US‐guided FNAC has its limitations because of low sensitivity in primary localization of the parathyroid adenoma in cases of primary hyperparathyroidism and is not a useful mode of investigation in cases of PA. Diagn. Cytopathol. 2009. © 2009 Wiley‐Liss, Inc.     

Fine‐needle aspiration of the Warthin‐like variant of papillary thyroid carcinoma: A report of three cases

In English literature, there are only few reports of Warthin‐like papillary thyroid carcinoma. We presented three cases and provided clinical, grossing, cytological, and histological correlation. In our point of view, the diagnosis of Warthin‐like papillary thyroid carcinoma is feasible based on cytomorphological aspects. Usually those cases present moderately or highly cellular smears with many atypical Hürthle cells showing obvious papillary thyroid carcinoma nuclear features and without papillary structures, even if the inflammatory background is mild.     

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.     

Fine‐needle aspiration of the diffuse sclerosing variant of papillary thyroid carcinoma masked by florid lymphocytic thyroiditis; A potential pitfall: A case report and review of the literature

The diffuse sclerosing variant of papillary thyroid carcinoma (DSV–PTC) is a rare tumor with aggressive behavior that requires aggressive treatment. Despite characteristic clinical and histological features that easily permit diagnosis, pre‐operative fine‐needle aspiration cytology (FNAC) diagnosis is often challenging and thus delays diagnosis. We describe the cytological features of a case of DSV–PTC diagnosed by FNAC in a 30‐year‐old woman presenting with an ill‐defined mass in her neck lasting for 2 months. Ultrasonograpy revealed a heterogeneous enlargement of both thyroid lobes suspicious for a lymphoproliferative syndrome. Flow cytometry showed a suspect B‐lymphocyte population. FNAC showed in five out of six slides an overwhelming presence of slightly atypical monomorphic small lymphocytes. The remaining slide showed syncytial tissue fragments of follicular cells with nuclear enlargement and pleomorphism, irregular nuclear membrane, grooves with scattered intranuclear inclusions, squamous metaplastic epithelium, and abundant psammoma bodies. A diagnosis of DSV–PTC was rendered and confirmed by total thyroidectomy and lymph node dissection. Our report supports the possibility of obtaining a preoperative diagnosis of DSV–PTC by FNAC. In the case of diffuse thyroid enlargement, adequate sampling of the thyroid and the presence of the combination of features described in our case permitted the diagnosis of this PTC variant. Diagn. Cytopathol. 2009. © 2009 Wiley‐Liss, Inc.     

Neuroendocrine carcinoma diagnosis from bile duct cytological specimens: A retrospective single‐center study

Neuroendocrine carcinoma (NEC) in the extrahepatic bile duct is extremely rare and clinically aggressive. Cytological examination of bile and/or bile duct brushing specimens plays an important role in the diagnosis of carcinoma of the extrahepatic bile duct, but only a few articles have described the cytological features of NEC in this area. Thus, we retrospectively analyzed the cytological features of NEC in bile and/or bile duct brushing specimens. Patients with a histopathological diagnosis of NEC who underwent bile and/or bile duct brush cytological examination were enrolled in this study. The cytological features, including the background, arrangement, and shape of the neoplastic cells, and nuclear and cytoplasmic features were reviewed. Six patients with small cell NEC were enrolled, and two of them had pancreatic tumors directly invading the bile duct wall. The cytological specimens showed small and/or large neoplastic cell clusters with occasional single cells in all cases. The 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 in all cases. One case had an adenocarcinoma component, which was also present in the cytological specimen. Cytological examination of bile and/or bile duct brushing specimens can be useful for the diagnosis of small cell NEC. This is an extremely rare but aggressive carcinoma, and its diagnosis by identifying characteristic cytological features may facilitate early detection and treatment.     

Osteoclast‐rich undifferentiated carcinoma of the urinary tract: Cytologic findings and literature review

The association of urothelial carcinoma with osteoclast‐like giant cells is an exceptionally rare event. To our knowledge, there are no published reports of the cytopathologic characteristics of osteoclast‐rich undifferentiated carcinoma of the urinary tract. We report herein, the case of a 63‐year‐old man who was evaluated at The Johns Hopkins Hospital for gross hematuria of 4 months duration. Urinary cytology displayed high‐grade malignant cells with scattered osteoclast‐like giant cells in a background of acute inflammation and abundant red blood cells. Subsequently, a transurethral tumor resection was performed, which revealed infiltrating undifferentiated carcinoma with osteoclast‐like giant cells. The rarity of this neoplasm and its resemblance to other giant cell‐rich processes may pose diagnostic difficulties. A review of the important differential diagnoses is also presented. Diagn. Cytopathol. 2010. © 2009 Wiley‐Liss, Inc.     

Mucinous breast carcinoma with myoepithelial‐like spindle cells

Appearance of spindle cells has been believed as a benign index of breast cytology. But, we have frequently observed the spindle cells in smears from mucinous carcinoma of the breast. Here, we characterized the biochemical nature of the spindle cells, so as to clarify their identity in cytology. Nineteen cases of breast mucinous carcinoma were used for cytological examination. The spindle cells were located at edges of tumor cell nests and in the backgrounds of cytological specimens. Immunohistological examination revealed that the spindle cells exhibited both immunoreactivity against carcinoembryonic antigen (CEA) and epithelial membrane antigen (EMA). Immunoreactivity against vimentin, cytokeratin, or alpha‐smooth muscle actin was, however, not observed. The mode of distribution of biochemical markers suggests that the positive cells for anti‐CEA antibody and anti‐EMA antibody are tumor cells compressed by mucin, while the vimentin‐positive cells are fibroblasts. We assert that the presence of spindle cells can be a characteristic feature of mucinous carcinoma of the breast. Discrimination of the spindle cells in mucinous carcinoma from myoepithelial cells and naked bipolar nuclei in benign lesions was established here. It should facilitate precise diagnosis of breast cancer. Diagn. Cytopathol. 2009. © 2009 Wiley‐Liss, Inc.     

High‐grade epithelial‐myoepithelial carcinoma of the parotid gland with mucous cell differentiation

Epithelial‐myoepithelial carcinoma (EMC) is a rare salivary gland tumor with a low‐grade malignancy, and EMC with high‐grade histopathological features is exceedingly rare. Furthermore, EMC with intracellular mucin is also extremely rare. We report an uncommon case of a high‐grade EMC of the parotid gland with mucous cell differentiation in a 66‐year old Japanese woman who noticed a right palpable parotid mass increasing in size within a one‐year period. The cytological specimen showed a focally biphasic structure and included isolated or discohesive piled‐up clusters with hyaline globules surrounded by neoplastic cells with nuclear atypia. The gross examination revealed a relatively well‐demarcated, multinodular gray‐whitish and solid mass. Histologically, the tumor consisted of variably sized solid nests or trabeculae with central necrosis and increased mitotic activity, and invaded into adjacent skeletal muscles. Immunohistochemically, the biphasic ductal and myoepithelial differentiation of this tumor confirmed the diagnosis of high‐grade EMC. Furthermore, numerous small nests with d‐PAS and alcian blue‐positive mucous cells predominated in about 5% of the whole tumor, and these mucous cells were encompassed by neoplastic myoepithelial cells. We should recognize this variant of EMC because we can't rule out the possibility of EMC even in the presence of mucous cells.     

Lymphoepithelioma‐like carcinoma of cervix

Lymphoepithelioma‐like carcinoma (LELC) is a rare neoplasm of the cervix. The importance of distinguishing this undifferentiated carcinoma with a predominant lymphocytic infiltrate lies in the fact that despite being poorly differentiated they have a better prognosis. The diagnosis however becomes more challenging when the pathologist is provided with a small cervical biopsy or a Papanicolaou smear. While the reports describing histology and their relation to Epstein–Barr virus (EBV) are many, there are only few case reports describing the cytology of these tumors. We describe the cytological features of LELC of cervix on conventional smear and correlate it with the histopathological findings of the same. A 67‐year‐old multiparous Hindu woman presented to the gynecology outpatient department with the history of postmenopausal bleeding for the past six months. The cytological examination of the cervical smear (Papanicolaou stain) was done followed by cervical and endometrial biopsy. Based on Papanicolaou smear and biopsy suggestive of a poorly differentiated carcinoma a radical hysterectomy with pelvic lymphadenectomy was performed. Hysterectomy specimen showed the morphology of LELC and was then correlated with the cervical smears retrospectively. On review of cytological smears it was seen that the tumor cell clusters had an abundant lymphoid background, which was overlooked earlier. Immunohistochemistry for EBV was negative. We conclude that the presence of undifferentiated tumor cell clusters with ill‐defined cell borders and large number of lymphoid cells in the background suggest the diagnosis of LELC on cervical cytology. Diagn. Cytopathol. 2017;45:239–242. © 2016 Wiley Periodicals, Inc.     

Differentiating cytological features of bronchioloalveolar carcinoma from adenocarcinoma of the lung in fine-needle aspirations: A statistical analysis of 27 cases

Bronchioloalveolar carcinoma (BAC) is an uncommon type of lung carcinoma that is important to distinguish from adenocarcinoma (adenoCA) because of its different biological behavior. Although the features of BAC have often been described in cytological material other than fine-needle aspirations (FNA), they have rarely been detailed in FNA specimens. We undertook to delineate the differentiating cytological features of 13 cases of BAC (7 of the nonsecretory type and 6 of the secretory type) and of 14 cases of bronchogenic adenoCA in FNA material, looking at 17 cytological criteria and using statistical analysis. When statistically analyzed with chi-square and Pearson's correlation, only 3 of the 17 features were found to be good discriminants for distinguishing nonsecretory BAC (NS-BAC) from adenoCA: prominence of monolayered tumor sheets, fine chromatin pattern, and mild cellular pleomorphism correlated significantly with NS-BAC. On the other hand, only the prominence of nuclear grooves and the abundance of extracellular mucin correlated significantly with secretory BAC (S-BAC) when compared to adenoCA. When using a logistic regression analysis, NS-BAC and S-BAC were best discriminated from adenoCA by the prominence of monolayered tumor sheets and by the abundance of extracellular mucin, respectively. We conclude that, in most instances, it is possible to make an accurate diagnosis of BAC and to distinguish it from adenoCA of the lung in FNA material. Diagn. Cytopathol. 16:253–257, 1997. © 1997 Wiley-Liss, Inc.     

Distribution of Lgr5‐positive cancer cells in intramucosal gastric signet‐ring cell carcinoma

Leucine‐rich repeat‐containing G‐protein‐coupled receptor 5 (Lgr5) is a putative intestinal stem cell marker that is also expressed in various tumors. To analyze its pathological characteristics in mucosal gastric signet‐ring cell carcinoma (SRCC), we investigated Lgr5 expression in 35 intramucosal gastric SRCC patients using RNAscope, a newly developed RNA in situ hybridization technique. Lgr5 expression in individual tumor cells was scored semi‐quantitatively from 0 to 400. Ki67 was also examined by immunohistochemistry, with a linear arrangement of Ki67‐expressing cells present in 20 of 35 cases. This area of Ki67‐expressing cells was topographically divided into upper, middle, and lower regions. All cases with linear Ki67 expression patterns also had Lgr5‐positive cells arranged in a linear fashion in the lower area—which was distinct from the area of high Ki67 expression. The rate of Ki67 positivity in Lgr5‐positive cells was significantly lower than that of Lgr5‐negative cells in areas of high Ki67 expression. In intramucosal SRCC, the low mitotic activity of Lgr5‐positive cells suggests that they may represent cancer stem cells as seen in other types of stomach carcinomas. Intramucosal SRCC may therefore contain stem cells expressing Lgr5 in the lower area of the lamina propria, akin to normal gastric pyloric mucosa.     

Two cases of adenocarcinoma in situ arising in lobular endocervical glandular hyperplasia indicating localization of mucin on the cluster surface as an early cytological finding of malignant transformation

Lobular endocervical glandular hyperplasia (LEGH) is an endocervical glandular hyperplastic lesion containing pyloric gland‐like mucin, and has recently been recognized as a precursor lesion of malignant glandular lesions of the endocervix. The pyloric gland‐like mucin contained in LEGH and gastric‐type adenocarcinoma is observed as golden‐yellowish by Papanicolaou staining. However, to our knowledge, the chronological course of the endocervical cytology of LEGH, eventually resulting in malignancy, has never been demonstrated to date. Here, we report two cases of gastric‐type adenocarcinoma in situ (AIS) arising in LEGH, together with an analysis of their cytological course. In both cases, localization of mucin on the surface of glandular cell clusters was observed prior to nuclear atypia in endocervical cytology. In addition, the diagnosis of gastric‐type AIS arising in LEGH was confirmed by pathological diagnosis of hysterectomy specimens in both cases. Histologically, all glandular cells of the LEGH without nuclear atypia contained a large amount of PAS‐positive mucin. On the other hand, in atypical glandular cells, localization of the mucin on the luminal surface was observed, although mucin was abundant throughout the cytoplasm in some areas. Our cases show the course of acquirement of cytological atypia of LEGH, and indicate the significance of localization of mucin on the surface of glandular cell clusters as an early finding of the malignant transformation of LEGH in endocervical cytology. Our results indicate that the distribution of mucin in glandular cells should be analyzed together with nuclear atypia in the endocervical cytology of suspected cases of LEGH.     

Pulmonary neuroendocrine tumors: An entity in search of cytologic criteria

Pulmonary neuroendocrine tumors (PNET) are histologically subclassified into typical carcinoid (TC), atypical carcinoid (AC), large cell neuroendocrine carcinoma (LCNEC), and small cell carcinoma (SCLC). The criteria for subclassification in cytological specimens are not well defined. In this study, we reviewed histologically confirmed 18 TC, 8 AC, 10 LCNEC, and 10 SCLC cytologic specimens from 45 patients. The following features were reviewed: small clusters, geographic sheets, trabecular structures, pseudo‐rosettes, single cells, doublets, triplets or short cords, papillary‐like structures, capillary vasculatures, necrosis, smear background, cell size, cell pleomorphism, amount of cytoplasm, plasmacytoid cells, spindle cells, nuclear atypia, molding, palisading and smearing, chromatin textures, nucleoli, and mitotic figure count. Based on our results, geographic clusters and necrosis were often seen in LCNEC and SCLC; while AC only showed scattered single cell necrosis. TC and AC commonly exhibited trabecular structures. Papillary‐like structures and capillary vasculature were only present in TC, AC, and LCNEC. Cells forming doublets, triplets, and short cords were more commonly seen in SCLC and rarely seen in other entities. Plasmacytoid and spindle cells were only seen in TC and AC. Nuclear smearing was not identified in TC, rare in AC, focally present in LCNEC and obvious in SCLC. Mitotic figures were nearly absent in TC, ≤5/10 HPF in AT, and ≥10/10 HPF in SCLC. LCNEC showed a wide span of mitotic count ranging between 2 and 16/10 HPF. In this study, we propose a set of cytological features that are essential for subclassification of PNETs in cytologic specimens. Diagn. Cytopathol. 2013;41:689–696. © 2013 Wiley Periodicals, Inc.