Detection of a strongly negative surface potential at Saturn's moon Hyperion.

On 26 September 2005, Cassini conducted its only close targeted flyby of Saturn's small, irregularly shaped moon Hyperion. Approximately 6 min before the closest approach, the electron spectrometer (ELS), part of the Cassini Plasma Spectrometer (CAPS) detected a field-aligned electron population originating from the direction of the moon's surface. Plasma wave activity detected by the Radio and Plasma Wave instrument suggests electron beam activity. A dropout in energetic electrons was observed by both CAPS-ELS and the Magnetospheric Imaging Instrument Low-Energy Magnetospheric Measurement System, indicating that the moon and the spacecraft were magnetically connected when the field-aligned electron population was observed. We show that this constitutes a remote detection of a strongly negative (∼ -200 V) surface potential on Hyperion, consistent with the predicted surface potential in regions near the solar terminator.

Anti-planetward auroral electron beams at Saturn.

Strong discrete aurorae on Earth are excited by electrons, which are accelerated along magnetic field lines towards the planet. Surprisingly, electrons accelerated in the opposite direction have been recently observed. The mechanisms and significance of this anti-earthward acceleration are highly uncertain because only earthward acceleration was traditionally considered, and observations remain limited. It is also unclear whether upward acceleration of the electrons is a necessary part of the auroral process or simply a special feature of Earth's complex space environment. Here we report anti-planetward acceleration of electron beams in Saturn's magnetosphere along field lines that statistically map into regions of aurora. The energy spectrum of these beams is qualitatively similar to the ones observed at Earth, and the energy fluxes in the observed beams are comparable with the energies required to excite Saturn's aurora. These beams, along with the observations at Earth and the barely understood electron beams in Jupiter's magnetosphere, demonstrate that anti-planetward acceleration is a universal feature of aurorae. The energy contained in the beams shows that upward acceleration is an essential part of the overall auroral process.

Galileo magnetometer measurements: a stronger case for a subsurface ocean at Europa.

On 3 January 2000, the Galileo spacecraft passed close to Europa when it was located far south of Jupiter's magnetic equator in a region where the radial component of the magnetospheric magnetic field points inward toward Jupiter. This pass with a previously unexamined orientation of the external forcing field distinguished between an induced and a permanent magnetic dipole moment model of Europa's internal field. The Galileo magnetometer measured changes in the magnetic field predicted if a current-carrying outer shell, such as a planet-scale liquid ocean, is present beneath the icy surface. The evidence that Europa's field varies temporally strengthens the argument that a liquid ocean exists beneath the present-day surface.

Magnetic Field Signatures Near Galileo's Closest Approach to Gaspra.

Two large magnetic field rotations were recorded by the spacecraft Galileo 1 minute before and 2 minutes after its closest approach to the asteroid Gaspra. The timing and the geometry of the field changes suggest a connection with Gaspra, and the events can be interpreted as the result of the draping of the solar wind field around a magnetospheric obstacle. Gaspra's surface field is inferred to be within an order of magnitude of Earth's surface field, and its magnetic moment per unit mass is in the range observed for iron meteorites and highly magnetized chondrites. The location of the magnetic signatures suggests that perturbations are carried by waves in the magnetosonic-whistler mode with wavelengths between electron and ion gyro radii.

Europa's magnetic signature: report from Galileo's pass on 19 December 1996.

On 19 December 1996 as Galileo passed close to Jupiter's moon, Europa, the magnetometer measured substantial departures from the slowly varying background field of Jupiter's magnetosphere. Currents coupling Europa to Jupiter's magnetospheric plasma could produce perturbations of the observed size. However, the trend of the field perturbations is here modeled as the signature of a Europa-centered dipole moment whose maximum surface magnitude is approximately 240 nanotesla, giving a rough upper limit to the internal field. The dipole orientation is oblique to Europa's spin axis. This orientation may not be probable for a field generated by a core dynamo, but higher order multipoles may be important as they are at Uranus and Neptune. Although the data can be modeled as contributions of an internal field of Europa, they do not confirm its existence. The dipole orientation is also oblique to the imposed field of Jupiter and thus not directly produced as a response to that field. Close to Europa, plasma currents appear to produce perturbations with scale sizes that are small compared with a Europa radius.

Magnetic field studies of the solar wind interaction with venus from the galileo flyby.

During the 10 February 1990 flyby of Venus, the Galileo spacecraft skimmed the downstream flank of the planetary bow shock. This provided an opportunity to examine both the global and the local structure of the shock in an interval during which conditions in the solar wind plasma were quite steady. The data show that the cross section of the shock in planes transverse to the flow is smaller in directions aligned with the projection of the interplanetary magnetic field than in directions not so aligned. Ultralow-frequency waves were present in the unshocked solar wind, and their amplitude peaked when the spacecraft was downstream of the foreshock. At large distances down the tail, the Mach number of the flow normal to the shock is low, thus providing the opportunity to study repeated crossings of the collisionless shock in an interesting parameter regime. Some of the shock crossings reveal structure that comes close to the theoretically predicted form of intermediate shocks, whose existence in collisionless plasmas has not been confirmed.

Estrogen receptor expression in benign breast epithelium and breast cancer risk.

BACKGROUND: Estrogen exposure is a major risk factor for breast cancer. Increased estrogen responsiveness of breast epithelium may enhance this effect. We examined the relationship between breast cancer diagnosis and 1) the presence and absence of estrogen receptor expression in benign breast epithelium, 2) the level of expression and 3) its variation during the menstrual cycle, and 4) other established risk factors. e.g., age, age at menarche, parity, and family history. METHODS: We measured estrogen receptor expression (as % of positive cells) by immunohistochemistry in normal breast epithelium from 376 women undergoing diagnostic or therapeutic breast surgery. Data on established risk factors were collected prior to surgery and those on menstrual cycle dates at the time of surgery. Logistic regression was used to assess risks (odds ratios [ORs]). RESULTS: The crude OR for breast cancer in women with estrogen receptor-positive breast epithelium versus those without was 3.16 (95% confidence interval [CI] = 1.89-5.28), with an OR of 2.49 (95% CI = 1.25-4.96) for premenopausal and an OR of 3.32 (95% CI = 1.43-7.68) for postmenopausal women. The ORs remained high and statistically significant after controlling for age and other breast cancer risk factors. The level of estrogen receptor expression was higher in patients with breast cancer than in control subjects and it was related to breast cancer risk in postmenopausal women (P trend <.005). Expression declined as expected in premenopausal control subjects as the menstrual cycle progressed but rose in breast cancer patients (P trend <.015). CONCLUSIONS: The overexpression of estrogen receptors in normal breast epithelium may augment estrogen sensitivity and hence the risk of breast cancer.

Field dipolarization in Saturn's magnetotail with planetward ion flows and energetic particle flow bursts: Evidence of quasi-steady reconnection.

We present a case study of an event from 20 August (day 232) of 2006, when the Cassini spacecraft was sampling the region near 32 RS and 22 h LT in Saturn's magnetotail. Cassini observed a strong northward-to-southward turning of the magnetic field, which is interpreted as the signature of dipolarization of the field as seen by the spacecraft planetward of the reconnection X line. This event was accompanied by very rapid (up to ~1500 km s-1) thermal plasma flow toward the planet. At energies above 28 keV, energetic hydrogen and oxygen ion flow bursts were observed to stream planetward from a reconnection site downtail of the spacecraft. Meanwhile, a strong field-aligned beam of energetic hydrogen was also observed to stream tailward, likely from an ionospheric source. Saturn kilometric radiation emissions were stimulated shortly after the observation of the dipolarization. We discuss the field, plasma, energetic particle, and radio observations in the context of the impact this reconnection event had on global magnetospheric dynamics.

Oestrogen receptor expression in normal breast epithelium.

Higher levels of oestrogen receptor (ER) expression in normal breast epithelium may compound the increase in breast cancer risk seen with prolonged estrogen exposure. In prior studies, we have used immunohistochemical ER assays on fresh frozen samples of benign breast tissue. Future studies will be more feasible on paraffin-embedded samples, and newer, more sensitive antibodies are now available. We examined 30 samples of paraffin-embedded breast epithelium from postmenopausal women with two antibodies, 6F11 and TE111. We find that the median labelling indices for ER are significantly higher using these antibodies, compared with previous results. The threshold for ER positivity will, therefore, have to be reset in future studies, since there are still many issues that remain to be resolved in this area.

Heterologous elements in the dedifferentiated component of dedifferentiated liposarcoma.

Five cases of dedifferentiated liposarcoma in which heterologous elements were present in the dedifferentiated component are presented. Two patients, men 54 and 66 years of age, had retroperitoneal atypical lipomatous tumors (well-differentiated liposarcomas) that recurred (after 2.5 and 12 years, respectively) as dedifferentiated liposarcomas with rhabdomyosarcomatous elements in the dedifferentiated components. The third patient, a 63-year-old woman, had a retroperitoneal dedifferentiated liposarcoma whose dedifferentiated component demonstrated focal osteoid formation. The fourth patient, a 36-year-old woman, had two seemingly separate retroperitoneal masses, one composed of atypical lipomatous tumor with foci of smooth muscle and the other of leiomyosarcoma; despite the apparent separation, it was thought more logical to consider this a dedifferentiated liposarcoma with leiomyosarcoma as the dedifferentiated component than two unrelated neoplasms. The fifth patient, a 45-year-old man, had a mediastinal dedifferentiated liposarcoma with angiosarcomatous areas in the dedifferentiated component. The relatively short follow-up thus far available on these cases has not demonstrated tumor behavior significantly different from that of dedifferentiated liposarcoma as a whole.

Diagnosing primary and metastatic renal cell carcinoma: the use of the monoclonal antibody 'Renal Cell Carcinoma Marker'.

The diagnosis of primary or metastatic renal cell carcinoma (RCC) can be difficult, especially in small biopsies, because of the wide variety of histologic appearances and clinical presentations that RCC can assume. An immunomarker specific for RCC is currently not available. We tested the relevant diagnostic use of the Renal Cell Carcinoma Marker (RCC Ma), a monoclonal antibody, against a normal human proximal tubular brush border antigen. Immunostaining using RCC Ma and the avidin-biotin-peroxidase complex technique was performed on archival tissues from primary and metastatic tumors of renal or nonrenal origin. A total of 122 of 153 primary RCCs (79.7%) were positive [clear cell (84%), papillary (96%), chromophobe (45%), sarcomatoid (25%), and collecting duct (0%)], with > or =10% of tumor cells stained in 93% of cases. None of the 64 primary renal tumors other than RCC, including 15 oncocytomas, was positive. Fifteen of 146 (10.2%) nonrenal primary tumors were positive (5 of 17 breast tumors, 8 of 8 parathyroid adenomas, and 2 of 7 embryonal carcinomas). Forty-two of 63 (67%) metastatic RCCs were positive with > or =10% of cells being stained in 83% of them. Two of 108 (2%) metastases from tumors other than RCCs were positive, both of which were metastatic breast carcinomas; however, only 10% (2 of 19) of metastatic breast carcinomas were positive. RCC Ma is an excellent marker for primary RCC, which should facilitate its diagnosis in a small biopsy. Although RCC Ma remains highly specific (98%) for metastatic RCC, a negative result may not rule out metastatic RCC because of a rather low sensitivity and a focal staining pattern in some of the positive cases. RCC Ma may also facilitate the differential diagnosis between oncocytoma and other types of RCC when they are composed mostly of eosinophilic cells.

The clinical application and cost analysis of fine-needle aspiration biopsy in the diagnosis of mass lesions in sarcoidosis.

BACKGROUND: Sarcoidosis is a prevalent disease of unknown cause characterized by granulomatous inflammation that often creates deep and/or superficial mass lesions. Tissue samples are considered the "gold standard" in diagnosis; however, it is a medically treated disease. We analyzed the utility and relative cost-effectiveness of fine-needle aspiration biopsy (FNAB) in the clinical investigation of patients with both suspected and unsuspected sarcoidosis. METHODS: All FNAB cases with sarcoidosis either as the cytologic diagnosis or mentioned as part of the differential diagnosis were retrospectively reviewed for clinical history, follow-up, cytologic features, and surgical pathology findings. Comparative analysis of cost of FNAB and excisional biopsy were also made. RESULTS: Thirty-two FNABs in 28 patients included 17 women and 11 men. Anatomic sites included lymph node (n = 17), lung (n = 5), salivary gland (n = 8), and liver (n = 2). Sarcoidosis had already been diagnosed or was a clinical consideration prior to FNAB in 14 cases. Chest radiograph showed abnormal findings in 19 cases. Angiotensin-converting enzyme (ACE) was measured in seven patients and was elevated in four. All aspirates showed granulomatous inflammation; in 22 patients, special stains or cultures for microorganisms were negative. Simultaneous or subsequent excisional biopsies confirmed the FNAB findings in 17 patients. Institutional ratios of excisional biopsy to FNAB in the diagnosis of sarcoidosis ranged from 4 to 19:1. The cost of FNAB was only 12.5 to 50% that of tissue biopsy. CONCLUSIONS: FNAB appears to be underutilized in the diagnosis of sarcoidosis. When used in conjunction with radiologic and laboratory data, FNAB may be a reliable and cost-effective method of diagnosis, especially in patients with an established diagnosis of sarcoidosis.

Is repeated fine-needle aspiration cytology useful in the management of patients with benign nodular thyroid disease?

Management of nonneoplastic thyroid nodules (TN) diagnosed by fine-needle aspiration (FNA) is controversial. While clinical follow-up with repeat FNA for enlarging TN is recommended in some studies, others recommend repeat FNA in follow-up of all benign TN after several months or years, in order to identify possible misdiagnosed malignant lesions. This study was done to determine the usefulness of repeat FNA in patients with benign nodular thyroid disease. We studied 94 fine-needle reaspirations performed on 43 females and 2 males 48.2 +/- 17 years of age with benign nodular thyroid nodular disease. Four patients had 3 consecutive FNAs and 41 patients had 2 consecutive FNAs. All FNAs were carried out by the same endocrinologist in the same thyroid area or by cytopathologists. The average time elapsed between the two consecutive FNAs was 18.3 +/- 11.2 (range, 4-48) months. Of the 45 patients, 23 presented with increase in size of the nodule and the remaining 22 patients did not have any change in size at the time of repeat FNA. Identical cytologic diagnoses were rendered in 39 of the 45 patients who underwent 2 or 3 consecutive FNA. Repeat FNA did not result in detection of any malignant neoplasms. Thyroid resection in 7 patients with increased nodule size and pressure symptoms confirmed the cytologic impressions of benign thyroid nodular disease. Our results show that the routine performance of repeated FNA cytology in the follow-up of patients with benign nodular thyroid disease with or without any clinical changes is of limited usefulness. Clinical factors rather than repeat FNA may hold precedence in surgical management of patients with benign nodular thyroid disease.

The role of fine-needle aspiration biopsy in the management of thyroid nodules in children, adolescents, and young adults: a multi-institutional study.

Thyroid nodules in children are extremely uncommon and in most cases present as asymptomatic neck masses. The significance of a thyroid nodule in a child involves the underlying risk of malignancy. The purpose of this study was to assess the validity of results of fine-needle aspiration biopsy (FNAB) of thyroid nodules in the pediatric population and its usefulness in pediatric patient management. FNAB was performed on a total of 57 thyroid nodules from 57 patients between 1992 and 1997. The patients included 46 females and 11 males ranging in age from 9 to 20 years (average 16.5 years). Surgical and/or clinical follow up was available in all patients. FNAB diagnoses included papillary thyroid carcinoma (PTC) (12.3% [7/57]), follicular neoplasm (FN) (15.8% [9/57]), atypical cytology (8.8% [5/57]) and nonneoplastic thyroid (63.2% [36/57]). Surgical follow-up available in all patients with cytological diagnoses of PTC, FN, and atypical cytology revealed malignancy in 13 cases. Of the 36 patients with nonneoplastic cytological diagnosis, surgical excision was performed in 3 patients and the rest were followed up clinically. Surgical excision in these 3 patients revealed follicular carcinoma (FC) (1 case) and multinodular goiter (2 cases). Overall, 14 patients (24.6%) had malignant thyroid lesions, including 11 PTC and 3 FC. In conclusion, the majority of pediatric thyroid nodules are benign. The prevalence of malignancy in pediatric patients with thyroid nodules in our series was 24.6%. High diagnostic accuracy of thyroid FNAB improves selection of pediatric patients requiring surgery.

The role of ultrasonography-guided fine-needle aspiration biopsy in the management of nonpalpable and palpable thyroid nodules.

The introduction of highly sensitive imaging techniques has made it possible to detect many nonpalpable thyroid nodules (non-PTN). We investigated the value of ultrasound-guided fine-needle aspiration biopsy (US-guided FNAB) as a diagnostic tool in the management of non-PTN as well as palpable thyroid nodules (PTN) that were considered difficult to aspirate without guidance. US-guided FNAB was performed on a total of 119 nodules (71 palpable and 48 nonpalpable) from 119 patients between 1992 and 1996. All available clinical and follow-up data were reviewed. Surgical follow-up was available in 24 cases. The patients included 100 females and 19 males ranging in age from 9 to 81 years (average, 51 years). FNA diagnoses (PTN versus non-PTN) included papillary carcinoma (12.7% [9/71] versus 4.2% [2/48], follicular neoplasm (16.9% [12/71] versus 0%), medullary carcinoma (1.4% [1/71] versus 0%), atypical cytology (5.6% [4/71] versus 2.1% [1/48], non-neoplastic thyroid (63.4% [45/71] versus 85.4% [41/48]) and unsatisfactory (0% versus 8.3% [4/48]). In 2 cases of occult papillary carcinoma, risk factors included radiation exposure (1 case) and a newly developed nodule during follow-up for hypothyroidism (1 case). Subsequent surgical follow-up (24 cases) confirmed the FNA findings, except for a case of Hürthle cell adenoma and 1 of Hashimoto's thyroiditis diagnosed as papillary carcinoma and follicular neoplasm, respectively. US-guided FNAB in most non-PTN are diagnosed as benign. For most patients with non-PTN and without any high-risk factors, a conservative approach such as clinical follow-up may be a more cost effective and logical approach. In contrast, US-guided FNAB is more useful in diagnosing biologically significant lesions in PTN that may be difficult to aspirate without guidance.

The role of fine-needle aspiration biopsy in the diagnosis and management of juvenile hemangioma of the parotid gland and cheek.

BACKGROUND: The current recommendation for the management of juvenile hemangiomas (JH) is to delay treatment in the hope of spontaneous regression. However, accurate diagnosis is necessary before considering conservative management. Traditionally, the diagnosis of JH has required excisional biopsy. The cytology literature on this relatively rare neoplasm is sparse. OBJECTIVE: To present our experience with fine-needle aspiration in the diagnosis and management of JH. DESIGN: Three cases with a cytologic diagnosis consistent with JH of the parotid gland and cheek were identified from our cytopathology files. Aspirate smears, immunohistochemical studies, computed tomographic scan findings, and clinical follow-up were reviewed. RESULTS: Patients were female infants ranging in age from 3 to 9 months and presented with an oval firm mass (size range, 2.0-5.0 cm) involving the parotid gland (2 cases) and cheek (1 case). Computed tomographic scan with contrast demonstrated homogeneous enhancement. Aspirate smears revealed spindle-shaped cells in sheets and clusters in a background of blood. The parotid gland aspirates and cell block preparations revealed ductal structures entrapped in sheets of spindle-shaped cells. Immunohistochemical studies revealed prominent vascular spaces lined by CD34 and factor VIII-positive flattened endothelial cells. The diagnosis of JH was rendered on the basis of the cytologic findings in conjunction with the radiologic and clinical findings. On clinical follow-up (8-24 months), none of the patients has shown any progression of the lesion. CONCLUSIONS: Fine-needle aspiration, in conjunction with imaging studies, is a useful tool in the diagnosis and management of JH. It eliminates the need for surgical excision for diagnostic purposes and allows for clinical follow-up of patients with JH.

Diagnostic utility of intracytoplasmic lumen and transgressing vessels in evaluation of Hürthle cell lesions by fine-needle aspiration.

INTRODUCTION: Recent abstracts have emphasized the importance of recognizing intracytoplasmic lumen and transgressing vessels as useful criteria enabling distinction between Hürthle cells encountered in neoplastic and nonneoplastic thyroid aspirates. The purpose of this retrospective study was to evaluate if application of these criteria improves specificity and sensitivity of cytologic diagnosis of true Hürthle cell neoplasms. MATERIALS AND METHODS: We retrospectively reviewed 30 fine-needle aspirates of thyroid with cytologic diagnosis of Hürthle cell neoplasms (13 cases) and nonneoplastic thyroid with prominent Hürthle cells (17 cases). All cases were evaluated for the presence of intracytoplasmic lumen and transgressing vessels and were reclassified as neoplastic or nonneoplastic based on the presence or absence of 1 or both of these criteria. Surgical follow-up was available in all cases. RESULTS: Surgical follow-up in 13 cases of Hürthle cell neoplasms revealed Hürthle cell carcinoma (3 cases), Hürthle cell adenoma (6 cases), and Hashimoto's thyroiditis (4 cases). Seventeen cases with nonneoplastic diagnosis revealed Hürthle cell carcinoma (1 case), Hashimoto's thyroiditis (12 cases), and nodular goiter (4 cases). After application of the previously mentioned cytologic criteria, the cytologic diagnoses were reclassified as Hürthle cell neoplasms (13 cases) and nonneoplastic thyroid (17 cases). The true sensitivity of the test before and after the application of the criteria was 90% and 100%, respectively. The true specificity before and after the application of the cytologic criteria was 65% and 85%, respectively. CONCLUSIONS: Intracytoplasmic lumen and transgressing vessels are helpful features in distinguishing neoplastic and nonneoplastic Hürthle cell thyroid lesions. Use of these criteria may improve the specificity and sensitivity of the cytologic diagnosis.

Ovarian neuroendocrine carcinoma associated with a mucinous neoplasm.

We describe a rare case of a neuroendocrine carcinoma of the ovary in a 22-year-old woman who presented with abdominal pain and a pelvic mass. Exploratory laparotomy revealed a right ovarian tumor weighing 2100 g. A right salpingo-oophorectomy and an appendectomy were performed. There was no evidence intraoperatively or postoperatively of metastatic disease. Microscopic examination of the ovary revealed solid nests of tumor cells with a neuroendocrine appearance, high mitotic rate, necrosis, and vascular invasion; the tumor was associated with a predominantly borderline mucinous neoplasm with a small focus of mucinous carcinoma. Neuroendocrine differentiation was confirmed by Grimelius stains, immunohistochemical assays (chromogranin), and electron microscopy. The appendix was histologically unremarkable. The patient received a course of chemotherapy; 3 months after completing chemotherapy, she developed multiple liver metastases and died of disease a week later. To our knowledge, this case report is the second one involving a primary neuroendocrine carcinoma of the ovary occurring in association with a mucinous neoplasm. Mixed mucinous and neuroendocrine carcinoma of the ovary may represent a rare neoplasm with extremely aggressive behavior.

Diagnostic accuracy and clinical utility of endoscopic bile duct brushing in the evaluation of biliary strictures.

Pathologic evidence of malignancy in biliary strictures is useful in the preoperative setting because it helps define therapeutic planning and prognosis. The purpose of this study was to assess the diagnostic accuracy and clinical utility of endoscopic bile duct brushings in the evaluation of bile duct strictures. We retrospectively evaluated 34 endoscopic biliary brushings derived from 31 patients with bile duct strictures. Relevant clinical and follow-up data were collected. Histologic specimens were reviewed in patients undergoing subsequent biopsies. Patients included 18 men and 13 women with an age range of 25 to 79 years (mean, 52 years). All patients had histologic and/or clinical follow-up. Cytologic diagnosis included cholangiocarcinoma (14.7%), suspicious for cholangiocarcinoma (5.9%), atypical hyperplasia (17.6%), and negative for malignancy (61.7%). All positive diagnoses were confirmed by histologic testing (false-positive rate, 0%). The cases that were suspicious for cholangiocarcinoma and the 5 atypical hyperplasia cases were also subsequently diagnosed as cholangiocarcinoma by biopsy. One atypical case was diagnosed as pancreatic carcinoma. All 21 negative cases were confirmed by biopsies (15) and clinical follow-up (6) (false-negative rate, 20%). Endoscopic bile duct brushing is diagnostically accurate and hence clinically useful in the management of patients with bile duct strictures. Atypical hyperplasias may contribute to diagnostic pitfalls leading to false-positive and false-negative diagnoses.

p53 immunolocalization in cell block preparations of squamous lesions of the neck: an adjunct to fine-needle aspiration diagnosis of malignancy.

OBJECTIVE: Mutations of the p53 tumor suppressor gene, with consequent nuclear p53 protein accumulation, are among the most common genetic abnormalities in human cancers. The purpose of this study was to determine the utility of p53 immunostaining as an adjunct to the diagnosis of malignancy in fine-needle aspirations of squamous lesions of the neck. MATERIALS AND METHODS: Using a monoclonal antibody to the p53 protein and a standard avidin-biotin complex technique, immunostaining was performed on paraffin-embedded cell blocks of 20 cases with the following cytologic diagnoses: (1) metastatic squamous cell carcinoma (SCC) (7 cases); (2) atypical squamous cells, SCC cannot be excluded (7 cases); and (3) cytologic findings consistent with branchial cleft cyst (6 cases). Tissue or clinical follow-up was available in all cases. RESULTS: Five (71%) of 7 cases with an unequivocal cytologic diagnosis of metastatic SCC were positive for p53 protein. Tissue follow-up confirmed metastatic SCC in all of these 7 cases. Of the 7 cases with cytologic diagnosis of atypical squamous cells, 2 were negative and 5 (71%) were positive for p53 protein. Subsequent excisional biopsies in these cases revealed metastatic SCC (6 cases) and branchial cleft cyst (1 case). The squamous cells in all 5 cases with cytologic findings consistent with branchial cleft cyst were negative for p53 protein; tissue follow-up confirmed the diagnoses of branchial cleft cyst in 4 cases. In the remaining 2 cases excision was not performed, as the cystic lesion was completely decompressed and, clinically, no recurrences were identified at 14 and 8 months of follow-up. CONCLUSIONS: Our findings suggest that p53 immunostaining is helpful in differentiating benign and malignant squamous lesions. While negative staining for p53 does not exclude malignancy, positive immunostaining may aid in accurate fine-needle aspiration diagnosis of malignancy in cytomorphologically equivocal squamous lesions of the neck.