Department of Pathology, The University of Texas MD Anderson Cancer Center, Texas
Corresponding author: Yun Gong, MD, Department of Pathology, Unit 53, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd, Houston, TX 77030; Fax: (713) 794-5664; firstname.lastname@example.org
Presented at the 60th Annual Scientific Meeting of the American Society of Cytopathology 2012; November 2-4, 2012; Las Vegas, NV.
Lymphoma with signet ring cell features (LSF) is a rare morphologic variant of non-Hodgkin lymphoma. Although it has been well documented in the surgical pathology literature, to the best of the authors's knowledge, the features of LSF in fine-needle aspiration (FNA) samples have rarely been reported. An accurate cytologic diagnosis of LSF is of important therapeutic significance.
The authors retrospectively reviewed 7 FNA cases of LSF for cytologic features, ancillary studies, corresponding histologic findings, and the patients' clinical and radiologic information to illustrate the diagnostic clues and potential pitfalls.
The final diagnoses, based on a multidisciplinary approach, were follicular lymphoma (5 patients), large B-cell lymphoma of follicular center cell origin (1 patient), and low-grade B-cell lymphoma with plasmacytoid features (1 patient). FNAs were obtained from both lymph node and extranodal sites. Common cytologic features included various percentages of signet ring cells in a background of nonvacuolated lymphomatous cells, lymphoglandular bodies, and cytoplasmic rings. The majority of signet ring cells contained a single, large, clear intracytoplasmic vacuole that pushed the nucleus laterally whereas fewer cells contained ≥ 2 vacuoles that indented the nucleus into a scalloped or stellate configuration. These cells resemble, to some degree, other lesions with signet ring cell features. One of the diagnostic clues of LSF was the similarity in nuclear details between signet ring cells and surrounding nonvacuolated lymphoid cells.
Lymphoma with signet ring cell features (LSF) is a rare morphologic variant of non-Hodgkin lymphoma in which the tumor tissue contains variable percentages of lymphocytes with a signet ring appearance. LSF is not a distinctive clinicopathologic entity, but rather a morphologic variant of different subtypes of lymphoma. Since its initial report in 1978 by Kim et al, a number of such cases have been described in the surgical pathology literature. The vast majority of these cases were non-Hodgkin lymphoma of follicular center cell origin,[1-7] although other types of non-Hodgkin B-cell lymphomas, and even T-cell lymphoma and CD30-positive anaplastic large-cell lymphoma, have also been documented.[8-11] However, to the best of our knowledge, the cytologic features of LSF have been only sparsely reported. To date, 7 single case reports have appeared in the cytology literature,[12-18] with only 5 of these cases being diagnosed in fine-needle aspiration (FNA) samples.[12-14, 16, 18]
FNA is a simple, fast, minimally invasive, cost-effective procedure that is often used as an initial diagnostic tool to evaluate primary or metastatic/recurrent tumors at virtually any site in the human body. However, for some types of lesions, a cytologic diagnosis based on an FNA sample may be more difficult to render than a histologic diagnosis because of the lack of reliable histologic architecture. For example, a back-to-back nodular growth pattern, which is a helpful histologic clue to the diagnosis of follicular lymphoma, is not readily appreciable on cytologic smears. In addition, unlike tissue biopsy which is more often used to sample primary tumors, FNA is more commonly used to sample metastatic tumors from various organ sites, sometimes metastatic tumors with an unknown primary source, which can make a correct cytologic diagnosis even more difficult. Misinterpretation of LSF as a metastatic carcinoma has been reported, even on histologic examination.
It is important to be aware of this morphologic variant of lymphoma in order to differentiate it from lesions that have similar cytologic features. Furthermore, familiarity with this variant of lymphoma helps to properly triage FNA specimens for ancillary studies during on-site immediate assessment and, more importantly, an accurate final diagnosis is of important therapeutic significance. In this study, we reviewed 7 FNA samples of LSF to illustrate the diagnostic clues and potential diagnostic pitfalls of this rare morphologic variant of lymphoma.
MATERIALS AND METHODS
The electronic database in the Department of Pathology at The University of Texas MD Anderson Cancer Center was retrospectively searched for cytologic cases that had a final diagnosis of LSF rendered from 2003 to 2012. Seven such cases were identified, all of which had slides available for review. During the FNA procedure, a 23-gauge or 25-gauge needle was used. For 6 patients, the procedure was performed by an interventional radiologist (2 of whom used sonographic guidance and 4 of whom used computed tomography guidance); for the other patient, the aspiration procedure was performed by a cytopathologist using palpation. Direct smears were air-dried for Diff-Quik staining (Statlab, Lewisville, Tex) and/or fixed in modified Carnoy fixative (a 6:1 ratio of 70% ethanol to glacial acetic acid) for Papanicolaou staining. For each case, the smears were assessed immediately by an on-site cytopathologist for sample adequacy and triage. In all 7 cases, aspirates were collected into RPMI medium, primarily for flow cytometry (FCM) immunophenotyping; an aliquot of cells in the RPMI medium was processed over Ficoll-Hypaque gradient (Pharmacia, Peapack, NJ) to enrich the mononuclear cells, which were then centrifuged onto glass slides as a cytospin preparation. The cytospin slides were used for immunocytochemical stains such as Ki-67 (for all 7 cases), DNA image analysis to assess proliferation index (for 3 cases), and fluorescence in situ hybridization (FISH) to detect the t(14;18)(q32;21) translocation (for 1 case).[19, 20] If the differential diagnosis during immediate assessment included an epithelial malignancy and/or an immunocytochemical workup was anticipated, an effort was made to obtain additional needle passes for cell block preparation whenever possible. For making the cell block (for 3 cases), a cell pellet obtained by centrifugation of the aspirates in the RPMI medium was fixed in a 1:1 mixture of 95% ethanol and 10% formalin, and then embedded in paraffin. We retrospectively reviewed each case for clinical and radiologic information of the patients, cytologic features of the FNA material, ancillary studies, and the histologic features of the concurrent or subsequent tissue biopsy. This study was approved by the MD Anderson Institutional Review Board.
The ages of the 7 patients ranged from 53 years to 81 years (mean, 68.2 years); 4 were men and 3 were women. Sites of FNA included the lymph nodes (4 patients, including 1 from mesenteric, 2 from retroperitoneal, and 1 from inguinal lymph nodes), vertebral bone (1 patient), hilar/lung mass (1 patient), and inferior auricular soft tissue (1 patient) (Table 1). Three of the 7 patients had a history of lymphoma (patients 1, 2, and 7). Concurrent or subsequent tissue biopsies of the corresponding tumors were available for 6 patients; however, 1 of the tissue biopsy samples was noncontributory due to a marked crush artifact. The final diagnoses, based on results of both FNA and tissue biopsy, were follicular lymphoma in 5 patients (1 of grade 1, 3 of grade 2, and 1 of grade 3), large B-cell lymphoma of follicular center cell origin in 1 patient, and low-grade B-cell lymphoma with plasmacytoid features in 1 patient.
Table 1. Clinical Information for the 7 Patients Diagnosed With Lymphoma With Signet Ring Cell Features and Corresponding Pathologic Findings
Location of Tumor
Immunophenotype by Flow Cytometry
DIA (Ploidy, Proliferation Index, % of Cells With DNA Content >5c)
Abbreviations: +, positive; −, negative; CD, cluster of differentiation; DIA, DNA image analysis; FISH, fluorescence in situ hybridization; FL, follicular lymphoma; LN, lymph node; sIg: surface immunoglobulin light chain restriction.
From time of the initial diagnosis of lymphoma to death or date of last follow-up.
sIg (kappa), CD19+, CD20+, FMC7+ (weak), CD10+, CD5−
Ki-67 of 40%, keratin-, CD20+
FL, grade 2
sIg (kappa), CD19+, CD20+, CD10+, BCL2+, CD5−
Ki-67 of 15%, keratin-, CD20+
Diploid, 0.5%, 0.0%
FL, grade 1
sIg (kappa), CD19+, CD20+, CD10+, CD5−
Ki-67 of 70%, CD20+
Diploid, 2.7%, 0.5%
FL, grade 3
sIg (kappa), CD19+, CD20+, FMC7+, CD10+, BCL6+, CD5−
Ki-67 of 20%
Large B-cell lymphoma, follicular center cell origin
sIg (kappa), CD19+, CD20+, CD10+, CD5−
Ki-67 of 32%
FL, grade 2
Lung, hilar mass
sIg (lambda), CD19+, CD20+, CD10+, CD5−
Ki-67 of 45%, keratin-, CD20+
Diploid, 2.8%, 0.4%
FL, grade 2
Inferior auricular mass
sIg (kappa), CD19+, CD20+, CD10-, CD5−
Ki-67 of 10%
B-cell lymphoma with plasmacytoid features, low grade
At the time of last follow-up, 4 patients were alive and 3 patients had died of disease. The median overall survival duration was 45 months (95% confidence interval, 27.6 months-80.4 months), and the 5-year overall survival rate was 43%.
Cytologic Features and Ancillary Studies
Smears from the 6 cases of lymphoma of follicular center cell origin were hypercellular, with single or loosely cohesive cell clusters of small to medium-sized lymphoid cells and various amounts of large lymphoid cells. The small to medium-sized lymphoid cells typically had scant cytoplasm and angulated, elongated, twisted, or cleaved nuclei with coarse chromatin and inconspicuous nucleoli, which is characteristic of centrocytes of follicular center origin. The large lymphoid cells had round to oval nuclei, vesicular chromatin, and 1 to 3 peripheral nucleoli, which is characteristic of centroblasts of follicular center cell origin. The percentage of large cells increased with tumor grade. The smears of the last case demonstrated a predominance of small-sized lymphoid cells with plasmacytoid differentiation.
In all cases, dispersed among the above-described cells were cells with intracytoplasmic vacuoles ranging in size from 1/3 to 1/10 of the cell body. The majority of these cells contained a single large vacuole that pushed the nucleus to 1 side or indented the nucleus, imparting a signet ring appearance; fewer cells contained ≥ 2 vacuoles that indented the nucleus into a scalloped or stellate configuration (Fig. 1). These cells accounted for 5% to 30% of the total cell number. The vacuoles appeared clear and empty and often had delicate sharp borders (Figs. 1-3). Some of the cells resembled histiocytes. The nuclear details of the signet ring cells, including the nuclear membrane, chromatin pattern, and nucleolus characteristics, were similar to those of adjacent nonvacuolated lymphoid cells (Fig. 2). In the background were numerous detached cytoplasmic fragments (ie, lymphoglandular bodies) as well as cytoplasmic “rings” devoid of nuclei. These structures were readily appreciable on Diff-Quik–stained cytospin preparations (Fig. 1). The cell block and core needle biopsy sections demonstrated corresponding findings (Figs. 3 and 4).
Ancillary studies with FCM and/or immunocytochemical staining were available for all 7 cases. Six cases demonstrated monotypic B-cells with surface immunoglobulin (Ig) light chain restriction that were positive for CD19, CD20, and CD10 and negative for CD5, which is consistent with lymphoma of follicular center cell origin. In 1 patient (patient 7; Table 1), the FCM showed a monoclonal B-cell population that was positive for CD19 and CD20 but negative for CD10 and CD5; the subsequent core needle biopsy sample was interpreted as low-grade B-cell lymphoma with plasmacytoid differentiation. The proliferation index determined by Ki-67 staining was consistent with the proliferation index determined by DNA image analysis in the 3 cases examined. As we observed in a previous study, the proliferation index was in keeping with the tumor grade. FISH was performed for patient 2, and the results demonstrated t(14;18)(q32;q21) translocation, a characteristic feature of follicular lymphoma. It is noteworthy that because of the presence of a few cellular clusters along with signet ring cells, the differential diagnosis included metastatic adenocarcinoma, and therefore pancytokeratin and CD20 immunostains were performed in 3 cases. In all 3 cases, the signet ring cells were negative for cytokeratin but positive for CD20.
To the best of our knowledge, the current study is, by far, the largest series of LSF diagnosed in FNA samples and illustrates the features that can help to ensure correct diagnosis. Consistent with published studies regarding LSF, the current series revealed that the most common type of lymphoma with signet ring cell morphology was lymphoma of follicular center cell origin, with various grade. It is noted that other types of non-Hodgkin lymphoma may also demonstrate similar signet ring cell features, such as small lymphocytic lymphoma, Burkitt lymphoma, immunoblastic lymphoma, diffuse large B-cell lymphoma, B-cell lymphoma with plasmacytic differentiation, Waldenstrom macroglobulinemia, multiple myeloma,[25, 26] and even T-cell lymphoma.[8-11]
The nature of the vacuoles in the signet ring cells has varied in different cases reported in the literature. Some investigators have stated that the vacuoles are an accumulation of monoclonal Ig that had been described as eosinophilic Russell body-like inclusions or hyaline globules in histologic sections, whereas others have described vacuoles as clear or empty.[1, 2, 6, 11, 13, 14, 16] Rarely, within the same lymphoma case, some signet ring cells contain hyaline inclusions and others contain clear vacuoles.[5, 7, 27]Using immunoperoxidase staining, Ramnani et al found that signet ring cells with hyaline globules displayed a greater intensity of staining with IgM and lambda light chain compared with nonvacuolated lymphoid cells. Harris et al, using IgG, IgA, IgM, and kappa and lambda light chain staining, did not observe convincing staining within the clear vacuoles. Accordingly, ultrastructural findings showed the cytoplasmic vacuole to be composed of either homogeneous, electron-dense material within dilated rough endoplasmic reticulum likely to be Ig or membrane-bound, electron-lucent spaces containing microvesicular bodies.[1, 2, 6, 7, 13, 26] In the current study, all 7 cases demonstrated clear empty vacuoles and no case was found to contain inclusions or globules.
The occurrence of LSF does not appear to be associated with any particular anatomic sites; both lymph node and extranodal sites have been described, although the nodal disease is more common. Reported extranodal sites include the skin, thyroid gland, salivary gland, mandible, tonsil, stomach, orbit, central nervous system, bone marrow,[34, 35] and urinary bladder.
The available data appear to indicate that the presence of signet ring cells in patients with lymphoma does not affect their prognosis and that the biological behavior and response to therapy are similar to those of corresponding subtypes of lymphoma without signet ring cell features.[1, 2, 5] Most studies describe an indolent clinical course and a long survival. Likewise, the median overall duration of survival for patients in the current series was 45 months. However, the significance of recognizing this rare variant of lymphoma is mainly to avoid an erroneous interpretation and to arrive at the correct diagnosis in a timely fashion, which is indeed of prognostic significance because patients can thereby receive timely and proper treatment. Familiarity with this morphologic variant of lymphoma could also help cytopathologists construct a reasonable differential diagnosis to consider during on-site immediate assessment so that aspirates can be triaged properly for further workup, such as FCM and FISH.
Because LSF is rare and can occur in any anatomic site, it is conceivable that this morphologic variant may cause diagnostic confusion and be mistaken for another type of malignancy, especially when a diagnosis is made based on FNA cytologic findings and clinical and/or radiologic information is not available. The differential diagnosis of LSF includes lesions that more frequently contain signet ring cells, such as metastatic adenocarcinoma with signet ring cell features, most commonly from the stomach and less commonly from the breast,[37, 38] prostate,[39-41] and/or lung. Other malignancies that may demonstrate signet ring cell features include squamous carcinoma, urothelial carcinoma, melanoma,[45-47] and liposarcoma.
When an LSF presents as a primary gastric lymphoma, differentiating between lymphoma and primary gastric signet ring cell carcinoma may be problematic. When LSF is found in a lymph node, the differential diagnosis is broader, ranging from the most commonly encountered metastatic signet ring cell adenocarcinoma to rarely occurring benign diseases such as sinus histiocytosis. We noted several morphologic clues pointing to a diagnosis of LSF.
The first clue is to recognize the underlying “neoplastic nature” of the background lymphoid cells. Although low-grade follicular lymphoma may cytologically resemble reactive lymphoid hyperplasia, a few subtle features may be indicative of a lymphomatous process, including the appearance of a relatively monotonous small to medium-sized lymphoid population with cleaved nuclei and a lack of apoptotic cells or tingible body macrophages. In high-grade lymphoma, the presence of numerous, large, atypical lymphoid cells makes the lymphomatous nature easier to recognize. Metastatic adenocarcinoma in a lymph node with lymphoma is quite unusual.
The second clue is to recognize the “lymphoid nature” of the signet ring cells. This can be facilitated by comparing the nuclear features and chromatin pattern of the signet ring cells with those of the surrounding nonvacuolated lymphoid cells and appreciating their close resemblance to each other.
The third clue is to recognize the “nonmucinous nature” of the vacuoles. In the current series, all the signet ring cells had clear, empty vacuoles rather than vacuoles with a viscous, mucinous appearance or inspissated mucin droplets (“targetoid cells”) that are characteristic of signet ring cell adenocarcinoma. We did not observe any of the hyaline inclusions described in other studies.
Finally, it is important to recognize cytoplasmic rings in the background. The rings likely represent pinched-off cytoplasm from signet ring cells and correspond to what Gilcrease et al described as “vacuoles and vacuolated structures” in the background, which is not supposed to be seen in signet ring cell adenocarcinoma. In addition, there is no mucin in the background.
Ancillary studies, including FCM, FISH, and immunocytochemical staining, are helpful for the differential diagnosis. The signet ring cells in lymphoma are negative for cytokeratin and mucicarmine but are positive for leukocyte common antigen and B-cell or T-cell lymphoma-specific markers.[3, 11, 16]
To distinguish LSF from metastatic melanoma with signet ring cell features in a lymph node, it is important to recognize that the nuclear features of melanoma cells are different from those of the surrounding lymphoid cells. Nonvacuolated melanoma cells typically demonstrate features such as binucleated cells, intranuclear pseudoinclusions, and prominent nucleoli. Melanoma with signet ring cell features may show cytoplasmic melanin pigments, and usually stain positive for melanocytic markers (S-100, HMB-45, and melan-A) but are negative for leukocyte common antigen and cytokeratin.
Liposarcoma should also be considered in the differential diagnosis, especially if a targeted LSF is in a retroperitoneal location and the signet ring cells contain clear, empty vacuoles. We noticed that intermingled among monovacuolated signet ring cells were a few multivacuolated cells, in which the nucleus was indented or scalloped by cytoplasmic vacuoles, simulating lipoblasts of liposarcoma. Similar multivacuolated cells were observed in some previous reports,[2, 13] but not in others. Three previously reported FNA cases of LSF and 2 cases in the current series were found in retroperitoneal lymph nodes.[12, 14, 18] It is noteworthy that, although liposarcoma should be considered in the differential diagnosis, the fact that liposarcoma rarely metastasizes to lymph nodes makes the occurrence virtually impossible. Furthermore, lipoblasts typically have dense, hyperchromatic nuclei with a chromatin pattern that differs from that of surrounding lymphoid cells. In difficult cases, ancillary studies should be helpful. Lipoblasts typically stain positive for Oil Red O and S-100, but are negative for leukocyte common antigen and other lymphoid markers.
Benign proliferations of histiocytes in the lymph nodes also may demonstrate signet ring-like features or contain multiple vacuoles and, therefore, should be included in the differential diagnosis.[48-50] However, although histiocytes may have an oval, grooved, folded, or indented nucleus, they typically have finely granular chromatin, an inconspicuous nucleolus, and a thin nuclear membrane, which differentiates histiocytes from lymphocytes. Histiocytes stain positive for CD68 and lysozyme but negative for leukocyte common antigen and other lymphoid markers.
In the current study, we described the cytologic features and results of ancillary studies to illustrate the potential diagnostic pitfalls of LSF in FNA samples. We emphasized the importance of recognizing this rare morphologic variant of lymphoma and including it in the differential diagnosis of other types of lesions with signet ring cell features. A multidisciplinary approach and appropriate ancillary studies are critical for reaching an accurate diagnosis.