Fine needle aspiration cytology of mammary carcinoma with choriocarcinomatous features: a report of 2 cases

BACKGROUND: Neoplasms of the breast containing multinucleated giant cells (MGCs) include both benign and malignant entities, such as benign soft tissue giant cell tumors, atypical fibrous histiocytoma, sarcomas, metaplastic carcinomas and the uncommon carcinomas containing osteoclast-like giant cells (OGC). Breast carcinoma with choriocarcinomatous features (BCCF) is a distinct variant of breast cancer. CASES: We report the cytologic features, pathologic findings and immunohistochemical profile in 2 cases of this unusual variant of breast carcinoma. Two women aged 53 and 50 years women presented with a history of left and right breast lump but no local lymphadenopathy, respectively. Fine needle aspiration cytology (FNAC) of both cases revealed abundant MGC with highly pleomorphic tumor cells in the hemorrhagic necrotic background. Both of the cases were histopathologically diagnosed as BCCF. CONCLUSION: Choriocarcinomatous differentiation with multinucleated syncytiotrophoblast-like giant cells is extremely rare in breast tumors. Although rare, FNAC of breast cancer with pleomorphic MGC requires careful search for differential diagnosis; breast carcinoma with giant cell features (choriocarcinomatous features, OGC features) must be differentiated from metastatic tumors and other breast lesions containing giant cells.     

Cystosarcoma phyllodes. Diagnosis by fine needle aspiration cytology.

The cytologic features of 10 benign, 2 borderline and 5 malignant phyllodes tumors were studied, and an attempt was made to correlate the cytologic findings with corresponding histologic categories. Seventy-five percent of the benign and borderline tumors were interpreted as benign cystosarcoma phyllodes on fine needle aspiration cytology. Eighty percent of the malignant phyllodes tumors were identified as malignant lesions cytologically. The cytologic features assessed were the epithelial:stromal ratio and morphology of the stromal component, including the degree of atypia, mitotic activity, capillary vessels traversing the stromal fragments, presence of foamy macrophages, histiocytic giant cells and bipolar naked nuclei. A diagnosis of phyllodes tumor was suggested cytologically by the presence of both epithelial and stromal elements; the stroma was present as cellular "phyllodes fragments" and isolated mesenchymal cells. The parameters suggesting malignancy were extreme paucity or absence of epithelial elements and stromal cells in diffuse sheets and clusters less cohesive than normal, with marked stromal atypia and mitotic activity.     

Cytology of nipple discharge in florid gynecomastia

OBJECTIVE: To determine the cytomorphologic spectrum of nipple discharge in florid gynecomastia. STUDY DESIGN: During a 22-year period (July 1979-June 2001), nipple discharge from nine males with breast lesions were examined. Smears from four of these cases with histologically documented gynecomastia were reviewed along with the tissue sections. RESULTS: In the three patients with florid gynecomastia the smears were cellular, with numerous benign ductal cells and papillary fragments along with foam cells and inflammatory cells. Epithelial atypia was mild in two cases and moderate in one. One of the three cases had an associated breast lump that showed features of florid gynecomastia on fine needle aspiration cytology. The biopsy from this case showed cystic hyperplasia of the breast similar to that in women with an intraductal papilloma. One case of simple gynecomastia on histology showed two fragments of benign ductal cells with occasional apocrine and foam cells. CONCLUSION: Nipple discharge in florid gynecomastia may pose problems in identification as the cellularity and atypia may lead to a misdiagnosis of carcinoma.     

Fine needle aspiration of breast lesions in women aged 30 and under

Fine needle aspiration (FNA) biopsies of 1,598 breast masses were performed between 1983 and 1989, and of them, 48 were from women aged 30 and under for whom a cytologic diagnosis was made by FNA and histologic follow-up was available. In 37 (77%) of the cases, both the cytologic and histologic diagnoses were benign. Fibroadenoma (20/37) and fibrocystic changes (14/37) were the most common benign lesions aspirated. Eight (17%) FNAs showed cytologic atypia. Four of these atypical lesions proved to be benign (two fibroadenomas, two fibrocystic changes). Epithelial proliferation in fibroadenomas and fibrocystic changes and cellular stroma in a fibroadenoma mimicking phylloides tumor were the causes of atypia in these biopsies. Four of the eight atypical lesions were shown to be carcinoma at biopsy (three infiltrating duct, one atypical medullary). Low cellularity, epithelial cohesiveness mimicking a fibroadenoma and background lactational changes in a pregnant patient were the causes of the atypical, rather than unequivocally malignant, diagnoses in these cases. In three patients (6%), a diagnosis of carcinoma was made by FNA and confirmed histologically (all were infiltrating duct carcinoma). Although most breast masses in women aged 30 and under are benign, cytologic atypia in a breast fine needle aspirate in this age group warrants a surgical biopsy. Clinical follow-up alone may be appropriate for young women with clinically nonsuspicious breast masses without cytologic atypia.     

Clinical and cytologic features of papillary neoplasms of the breast

OBJECTIVE: To compare the cytologic features benign and malignant papillary breast lesions. STUDY DESIGN: We reviewed the clinical and cytologic features in 29 cases of intraductal papilloma and 26 cases of atypical papilloma or papillary carcinoma that had been diagnosed by histologic examination. The diameter of the mass was examined as a clinical feature. The cytologic features evaluated were as follows: bloody background, row of tall columnar cells, naked bipolar nuclei, hemosiderin-laden macrophages, myoepithelial cells, single scattered atypical cells, cellularity, nuclear atypia, nuclear grade, apocrine metaplasia, eosinophilic cytoplasmic granules, papillary clusters, small papillae, cell balls and large sheets. RESULTS: Of the features evaluated, the diameter of the mass, naked bipolar nuclei and cell balls differed significantly between benign and atypical or malignant papillary neoplasms. The average diameter of a benign papillary neoplasm was 1.8 cm, and that of an atypical or malignant papillary neoplasm was 2.2 cm (p = 0.042). Naked bipolar nuclei were found in 27 cases of benign papillary neoplasm (93.1%) versus 19 cases of atypical or malignant papillary neoplasm (73.1%) (p = 0.050). Cell balls were found in 14 (48.3%) and 21 (80.8%) cases, respectively (p = 0.012). All 6 cases in which cell balls were present and naked bipolar nuclei were absent proved to be atypical or malignant papillary neoplasms. Of 17 cases in which cell balls were absent and naked bipolar nuclei present, 13 (76.5%) were benign papillary neoplasms. CONCLUSION: Most cytologic features overlapped in benign and atypical or malignant papillary neoplasms. Although they were not pathognomonic, naked bipolar nuclei and cell balls were cytologic features that differed significantly between benign and atypical or malignant papillary neoplasms. When papillary neoplasms of the breast are suspected in a cytologic smear, the combination of clinical examination, mammography and cytologic features should be considered to make the correct diagnosis.     

Cytomorphologic spectrum of carcinoma ex pleomorphic adenoma

OBJECTIVE: To delineate the cytomorphologic features of carcinoma ex pleomorphic adenoma (CPA) and identify the diagnostic pitfalls. STUDY DESIGN: Smears of 14 cases suspected as CPA on fine needle aspiration over a period of 15 years were reviewed. Cytohistologic correlation was done in 10 cases. RESULTS: All cases had a salivary gland mass of 1-16 years' duration, with a rapid increase in size in 10 cases. Epithelial cells predominated over stroma in 11 of 14 cases. Group I showed unequivocal malignant cells admixed with benign epithelial and stromal components of pleomorphic adenoma (PA), which were considered diagnostic of CPA on review. The cytologic differential diagnosis in these cases included mucoepidermoid carcinoma, carcinosarcoma and metastatic adenocarcinoma. Group II comprised 7 cases suspected to be cellular PA with atypia or CPA. These showed mild to moderate degrees of pleomorphism, absence of unequivocal malignant cells, and a variable proportion of benign epithelial and stromal components. Four of them were histologically confirmed as CPA. CONCLUSION: Sampling error is an important cause of diagnostic pitfalls. Correlation with clinical data is essential in diagnosis of CPA on cytology. In a proper clinical setting, extensive fine needle aspiration sampling should be done initially. Any degree of nuclear atypia in PA should be documented, alerting the clinician and histopathologist to the possibility of CPA.     

Gynecomastia: cytologic features and diagnostic pitfalls in fine needle aspirates.

OBJECTIVE: To illustrate some of the uncommon cytologic findings of gynecomastia, such as apocrine metaplasia, cellular atypia and foamy macrophages, that can be misinterpreted as evidence of malignancy. STUDY DESIGN: The clinical data and fine needle aspiration (FNA) cytologic material from 100 men with the diagnosis of gynecomastia were retrospectively reviewed. The excisional biopsy slides were available for 16 cases. For comparison, FNA smears from five men with breast lesions other than gynecomastia were studied. RESULTS: The patients ranged in age from 23 to 91 years. Cytologic findings were as follows: cohesive sheets of cells containing 20-1,000 cells (98%); scattered, single, bipolar cells (78%); spindle cells (68%); ductal epithelial atypia (26%); apocrine metaplasia (8%); and foamy histiocytes (12%). In nine cases the atypia was marked, and in two of them the possibility of malignancy could not be ruled out. Surgical follow-up on 16 patients, including the cases with marked atypia, showed gynecomastia. In one case, gynecomastia was associated with intraductal papilloma. No correlation between the underlying etiology and atypical cytologic features of gynecomastia was identified. CONCLUSION: Apocrine metaplasia and epithelial atypia are common findings in gynecomastia. Attention to the cell patterns, the presence of sheets of ductal cells and absence of atypical single cells will point to the correct diagnosis.     

Fine needle aspiration of benign and malignant breast masses associated with pregnancy.

Of 1,612 fine needle aspirates (FNA) of breast lesions performed over a seven-year period, 25 cases (1.5%) were identified as breast masses associated with pregnancy. Patients ranged in age from 16 to 46 years, with a mean of 27. Gestational age at the time of FNA ranged from three months to three months postpartum or following breast-feeding. Cytologic diagnoses of these pregnancy-associated breast masses were: galactocele (5 cases, 20%), lactating adenoma (9 cases, 36%), fibroadenoma with lactational change (7 cases, 28%), juvenile fibroadenoma with lactational change (1 case, 4%), atypical reactive duct cells with lactational change (1 case, 4%) and infiltrating duct carcinoma (2 cases, 8%). The degree of lactational change varied proportionately with gestational age. None of the 22 patients with benign cytologic diagnoses of galactocele, lactating adenoma or fibroadenoma subsequently developed carcinoma. The mean clinical follow-up for these 22 patients was 27 months. Three cases of fibroadenoma and the case of juvenile fibroadenoma were confirmed by surgical excision. Biopsy of the lesion cytologically diagnosed as atypical reactive duct cells with lactational change revealed infiltrating duct carcinoma (IDC). All three patients with IDC had involvement of multiple axillary lymph nodes, and 1 patient had widely metastatic disease. In two cases of IDC the background lactational breast epithelium exhibited marked cytologic atypia that closely resembled the IDC. Pregnancy-related cellular atypia potentially results in a false-positive diagnosis of breast carcinoma on FNA. FNA is useful in distinguishing benign breast masses of pregnancy from those with marked cytologic atypia requiring surgical biopsy and may minimize the delayed diagnosis of carcinoma associated with pregnancy.     

HIV-1 (p24)-positive multinucleated giant cells in HIV-associated lymphoepithelial lesion of the parotid gland. A report of two cases

BACKGROUND: Cystic benign lymphoepithelial lesion (CBLL) is a well-recognized parotid disorder the diagnosis of which can be made on the basis of clinical findings, human immunodeficiency virus (HIV) testing, image studies and fine needle aspiration (FNA). Most aspirations are cystic, and the lesion can be recognized if the triad of foamy macrophages, lymphoid and epithelial (squamous) cells is observed. CASES: The authors recently observed FNA cytologic features of two HIV-associated cases that exhibited numerous multinucleated giant cells (MGCs) but failed to show the epithelial component. A subsequent surgical resection was performed in one patient. Similarly to what has been described for nasopharyngeal (adenoid and tonsil) lymphoid tissue of HIV-positive patients, intense immunoexpression of S-100 and p24 (HIV-1) protein was present in MGC. CONCLUSION: The diagnosis of HIV-associated CBLL should always be considered if a parotid cystic lesion presents with numerous MGCs. Immunocytochemical detection of p24 (HIV-1) protein in MGC becomes a very useful diagnostic aid and extends to parotid CBLL many of those pathogenic features of HIV-1 infection already noted in other HIV-1-infected, lymphoid oropharyngeal lesions.     

Cytology of cystic nephroma: a case report

BACKGROUND: Cystic nephroma is a rare benign multiloculated cystic renal neoplasm that is often confused with multicystic renal cell carcinoma radiographically and cytologically. CASE: A 58-year-old woman was incidentally found to have a multiloculated cystic right renal lesion. Cytologic examination of the fluid aspirated from the lesion was reported as highly suspicious for renal cell carcinoma, but a right nephrectomy revealed a cystic nephroma. CONCLUSION: Cystic nephroma fluid is characterized by the presence of sparse epithelial cells with moderate nuclear atypia. Conversely, the fluid of multicystic renal cell carcinoma is moderately cellular with no or mild nuclear atypia.     

Fine needle aspiration of pancreatic cystic epithelial neoplasms.

Pancreatic cystic epithelial neoplasms present diagnostic challenges in cytology. An accurate diagnosis is important since the prognosis and treatment may vary. We report the cytologic features in fine needle aspirates of four cases of cystic neoplasms of the pancreas (two micro-cystic adenomas, one mucinous cystic neoplasm and one mucinous cystadenocarcinoma). Smears were evaluated as to their cellularity, content and predominant cell type. Aspirates from the microcystic adenomas yielded hypocellular material with rare strips of cuboidal cells having bland nuclei and pale cytoplasm. No mucinous material was identified in the background, but the cells stained positively with periodic acid-Schiff stain. Smears from the mucinous cystic neoplasm were moderately cellular and contained abundant mucinous material. The columnar epithelial cells were arranged in tight sheets, clusters and strips. Most cells had benign nuclear features with focal mild nuclear atypia. Key cytologic findings noted in the mucinous cystadenocarcinoma were moderate cellularity, loose clusters of cells, single cells, overt malignant nuclear features and occasional signet ring cells. Pancreatic pseudocysts can be distinguished from pancreatic cystic epithelial neoplasms by the predominance of histiocytes and inflammatory cells and absence or paucity of epithelial cells. To differentiate microcystic adenomas from mucinous cystic neoplasms, the above criteria coupled with periodic acid-Schiff and mucin staining should effectively differentiate these diagnostic entities.     

Fine needle aspiration cytology of radiation-induced changes in nonneoplastic breast lesions. Possible pitfalls in cytodiagnosis

The range of radiation-induced changes in fine needle aspiration (FNA) smears of the breast is described. In 41 of more than 800 patients who underwent breast-conserving treatment, a palpable breast lesion developed, and FNA was performed. In six cases, a recurrent carcinoma was present. In the remaining cases, three patterns of nonneoplastic lesions could be discerned: epithelial atypia (14 cases), fat necrosis (10 cases) and poorly cellular smears without epithelial atypia or fat necrosis (13 cases). It is important to be familiar with the patterns of radiation-induced epithelial atypia, since such atypia may lead to a misdiagnosis of recurrent carcinoma. These atypical cells may show impressive anisocytosis and anisonucleosis; however, the nuclear/cytoplasmic ratio remains normal and an admixture of bipolar cells is present. Cell dissociation and necrotic cell debris, as often seen in breast cancer smears, were never encountered in FNA smears from radiated nonneoplastic breasts.     

Comparative cytology of mucocelelike lesion and mucinous carcinoma of the breast in fine needle aspiration

OBJECTIVE: To study the fine needle aspiration cytology (FNAC) features of mucocelelike lesion (MLL) of the breast and to compare them to those of mucinous carcinoma. STUDY DESIGN: The fine needle aspiration (FNA) smears of 7 cases of histologically proven MLL (2 malignant and 5 benign, including 4 associated with atypical ductal hyperplasia) were reviewed and compared to those of 14 mucinous carcinoma cases. RESULTS: In all cases, grossly visible thick, mucoid material was obtained from FNA. The most important features for distinguishing benign MLL from mucinous carcinoma were: (1) scant cellularity; (2) no or rare single, intact tumor cells; (3) tumor cells arranged in cohesive monolayers; and (4) absence of significant nuclear atypia. In contrast, mucinous carcinoma in general showed higher cellularity; abundant single, intact cells; three-dimensional cellular clusters in most cases; and nuclear atypia ranging from mild to severe. CONCLUSION: Mucinous lesions of the breast should be divided into MLL and frank mucinous carcinoma based on FNAC. However, FNAC diagnosis of malignant MLL has yet to be defined. Excisional biopsy is advised for all hypocellular cases for further separation into benign and malignant MLL and to rule out the possibility of hypocellular mucinous carcinoma.     

Macrophage-rich reaction in lymph nodes as a mimic of metastatic renal cell carcinoma on fine needle aspiration. A case report

BACKGROUND: Renal cell carcinomas have a high metastatic potential. Many of them are occult at initial presentation and mimic a primary neoplasm of the metastatic site. However, not all lymph node enlargements in a patient with a history of renal cell carcinoma are due to metastasis. Foamy macrophages can mimic metastatic renal cell carcinoma cells. CASE: A 60-year-old male with a known diagnosis of renal cell carcinoma of clear cell type developed enlarged neck nodes 44 months after the diagnosis. These were aspirated to yield cystic fluid that, on smears, showed numerous clear cells with low nuclear grade. Immunohistochemical stains revealed these cells to be foamy macrophages (CD68 immunoreactive) and not metastatic renal cell carcinoma, as had been suspected on initial examination of Diff-Quik and Papanicolaou-stained smears. CONCLUSION: Immunohistochemistry is a valuable adjunct in avoiding a false diagnosis of metastatic carcinoma in macrophage-rich nodal reactions in patients with a history of renal cell carcinoma.     

Automated image morphometry of lobular breast carcinoma

OBJECTIVE: To analyze the role of automated image morphometry (AIM) in distinguishing infiltrating lobular carcinoma (ILC) of the breast from benign, borderline and infiltrating ductal carcinoma (IDC). STUDY DESIGN: Only histopathologically proven lobular carcinoma, ductal carcinoma, borderline lesions and benign breast lesions were selected for the study. There were 19 cases of ILC and 30 cases of IDC, 20 cases of benign lesions (fibroadenoma, 18; fibrocystic disease, 1; and fibroadenosis, 1); 10 cases were borderline lesions (mild epithelial hyperplasia, 3; moderate epithelial hyperplasia, 2; florid epithelial hyperplasia 4; intraductal papillary carcinoma, 1). In all cases hematoxylin and eosin-stained slides were used for AIM. At least 100 cells from each case were subjected to analysis randomly with an image cytometer with Leica Quantimet 600 software (Cambridge, England). Nuclear area, diameter, perimeter, convex perimeter, convex area and roundness were measured in each case with random, unbiased selection of cells and 40 x objectives (one pixel = 0.46 microm). AIM data on the cases were analyzed in relation to final cytologic diagnosis. RESULTS: All the nuclear morphometric features of ILC were much lower than those of IDC and borderline lesions, whereas nuclear morphometric data on ILC were only marginally more than those on benign cases. ANOVA showed that mophometric data were significant (P < .05) in all the variables between ILC and IDC. However, there was no significant difference between ILC, and borderline and benign cases. CONCLUSION: Image morphometry may be useful in distinguishing ILC from IDC on cytologic smears. However, morphometric data may not be helpful in distinguishing benign and borderline lesions from ILC.     

Metastatic breast carcinoma in cerebrospinal fluid. A cytomorphometric study

A study was undertaken to quantitate the cellular characteristics of metastatic breast carcinoma in cerebrospinal fluid (CSF). Millipore filters of CSF from 15 patients with metastatic breast carcinoma were reviewed; 50 cells per case were evaluated when available. All cells in all cases shed singly or in loose clusters; tight balls or morulae were absent. All cells had regular, round-to-oval nuclei with finely granular chromatin. The majority of cells in all cases had single or multiple round nucleoli, granular cytoplasm with distinct borders and a mean nuclear-cytoplasmic ratio of close to 0.70. Cellular background, number of tumor cells per case, number and placement of nuclei and nuclear and cytoplasmic diameter varied both within and among the cases. There was significant variation in nuclear and cytoplasmic diameters both within and among the cases of infiltrating ductal carcinoma. Thus, the uniform appearance of the cells was due to consistent cytologic features, not to similarity in cell size. The cytologic profile of metastatic breast carcinoma is sufficiently characteristic to distinguish this tumor from other benign and malignant lesions that shed in the CSF.     

Fine Needle Aspiration Cytodiagnosis of Apocrine Carcinoma of the Breast

The cytopathological appearances of 14 cases of apocrine breast carcinoma diagnosed by fine needle aspiration cytology are described and the features compared to those seen in apocrine cells aspirated from benign cystic and solid lesions. Significant atypia must be observed before a diagnosis of apocrine carcinoma can be entertained.     

Role of CD10 immunochemistry in differentiating hepatocellular carcinoma from metastatic carcinoma of the liver

Background:  Differentiation of hepatocellular carcinoma (HCC) from metastatic carcinoma in liver may be difficult on fine needle aspiration cytology (FNAC), especially when both appear as moderate to poorly differentiated tumours. A panel of immunocytochemical stains is frequently used in case of diagnostic difficulty. Recently, CD10 immunostain with a canalicular staining pattern has been shown to be a specific marker for hepatocytic differentiation.
Objective:  The present study was designed to assess the value of CD10 immunostain in distinguishing HCC from metastatic carcinoma in material obtained by FNAC of liver masses.
Materials and methods:  Formalin-fixed, paraffin-embedded cell blocks of 22 cases (7 cases of HCC and 15 cases of metastatic carcinoma), direct acetone-fixed smears and destained smears of 28 cases (18 cases of HCC and 10 cases of metastatic carcinoma) prepared from FNAC of the liver were immunostained using monoclonal antibody against CD10.
Results:  Seventeen (68%) of twenty-five cases of HCC were positive for CD10 with a canalicular staining pattern. Among them 7 (70%) of 10 cases were well-differentiated HCC and 10 (66%) of 15 cases were moderate to poorly differentiated HCC. Of 25 cases of metastatic carcinoma, four (16%) were positive for CD10 with a cytoplasmic (three cases) and membranous staining (one case) pattern.
Conclusion:  CD10 immunostaining is useful in discriminating HCC and metastatic carcinoma of the liver and is easily applied on cell blocks as well as FNAC smears.     

Reduced expression of Claudin-7 in fine needle aspirates from breast carcinomas correlate with grading and metastatic disease

OBJECTIVE: To study the immunocytochemical expression of the tight junction protein Claudin-7 in smears from breast carcinomas and correlate with grading, nodal status, locoregional and distant metastases and the cellular cohesion. METHODS: The material consisted of 52 air-dried smears from fine needle aspirates of breast carcinomas, both primary and metastatic and smears from seven benign lesions. A primary antibody to Claudin-7 was used for immunocytochemical staining. The degree of staining was recorded as negative, reduced or full, with full expression meaning equivalent to the staining pattern found in the fibroadenomas used as benign control. Staining intensity and the percentage of stained cells were evaluated. The control smears revealed a strong membrane and cytoplasmic positivity in all luminal epithelial cells. Cellular cohesion was graded as: (1) mainly cohesive groups, (2) groups and single cells and (3) mainly single cells. RESULTS: All primary and recurrent/metastatic breast lesions expressed Claudin-7. Full expression was demonstrated in 46% of the cases. Reduced expression was found in 54%. In cases with reduced expression, the percentage of stained cells were usually high, and no smear showed <50% stained tumour cells. The staining pattern was heterogeneous and always mixed membrane/cytoplasmic. Claudin-7 expression showed a significant correlation (P < 0.05) with grading, locoregional and distant metastases, nodal involvement and cellular cohesion in invasive carcinomas, but not with tumour size or subtype. CONCLUSION: Reduced expression of Claudin-7 correlated with higher tumour grade, metastatic disease, including loco-regional recurrences and with cellular discohesion.     

Syncytial giant cell component. Review of 55 renal cell carcinomas

Different types of multinucleated giant cells (MGC) have been documented in tumors with osteoclast-like appearance, with trophoblastic differentiation or as tumoral malignant giant cells. A new variety of MGC has been described in renal cell carcinoma. In order to study the frequency, nature and significance of this cellular type, we have reviewed our files. To assess the presence, nature and significance of these MGC in renal cell carcinomas and associated histologic subtype. To review all malignant renal tumors diagnosed in the last 5 years in our hospital and to carry out a morphologic and immunohistochemical study in renal cell carcinomas with syncytial type MGC. 55 renal cell carcinomas were reviewed. Clear cell (conventional) renal cell carcinoma was the most common type encountered (40 cases); two of these cases showed syncytial type MGC and low grade malignancy. Microscopically the MGC contained from 5 to 40 nuclei. Immunohistochemically, mononucleated and multinucleated cells were positive for cytokeratin CAM 5.2, cytokeratin AE1/AE3 and weakly positive for vimentin. Histiocytic, muscular, neural markers, beta-HCG and alpha-fetoprotein were negative. The presence of syncytial type MGC in renal cell carcinomas is an exceptional event. Among 55 renal cell carcinomas we found two cases, both of which were of clear cell subtype and low grade malignancy. The MGC proved positive for epithelial markers and probably are the result of mononucleated tumoral cell fusion. We are unaware of the impact of this MGC in the outcome of patients; such cells appear in low grade carcinomas and do not seem to be of dismal prognosis.