Warthin's tumor with malignant lymphoma. DNA analysis of paraffin-embedded tissue

Prevalence of Lymphoid Neoplasia in a Retrospective Analysis of Warthin Tumor: A Single Institution Experience

Warthin tumor is one of the most common benign salivary gland tumors. Overt lymphoma is known to occur in the lymphoid stroma of Warthin tumor. In situ follicular neoplasia is difficult to identify in routine histologic examination of lymphoid tissue and has not been reported in association with Warthin tumor. Our objective is to determine the prevalence of overt malignant lymphoma and in situ follicular neoplasia in Warthin tumor. We conducted a retrospective histological evaluation of 89 sequential Warthin tumor cases with available slides and blocks from the years 2010-2019. Of these, 84 cases were subjected to immunohistochemical testing, while 5 cases had been previously worked up for the suspicion of lymphoma. We identified two additional cases of lymphoid neoplasia associated with Warthin tumor including small lymphocytic lymphoma/chronic lymphocytic leukemia (n = 1) and in situ follicular neoplasia (n = 1) in addition to previously reported case of follicular lymphoma included in this study. The prevalence rate of first-time detected lymphoid neoplasia in Warthin tumor is 3.4%. The prevalence rate of overt lymphoma is 2.2%, while the prevalence of in situ follicular neoplasia is 1.1%. We propose histologic criteria to identify small lymphocytic lymphoma and follicular lymphoma in Warthin tumor. These include a monotonous interfollicular expansion of small lymphocytes and germinal centers composed of a monotonous population of lymphocytes without polarity or tingible body macrophages respectively. It is very important for pathologists to perform a diligent morphological examination and perform immunohistochemistry in suspected cases to identify subtle involvement of Warthin tumor by lymphoma. In patients with involvement of Warthin tumor by in situ follicular neoplasia, concurrent lymphoma in the same tissue and other sites should be considered. Patients without overt lymphoma elsewhere likely have a low risk of progression to follicular lymphoma. The low prevalence of in situ follicular neoplasia in Warthin tumor, combined with the low rate of clinical progression to lymphoma, make routine screening of Warthin tumor for in situ follicular neoplasia unnecessary.

Diffuse large B-cell lymphoma arising from follicular lymphoma with warthin’s tumor of the parotid gland - immunophenotypic and genetic features: A case report

BACKGROUND

Warthin’s tumor (WT) is composed of several cysts that are lined with tall, bilayered oncocytic columnar cells and lymphoid stroma. Within WT, the two components rarely transform into carcinoma or lymphoma, and when it does, carcinoma is the most common type. Approximately 28 cases of lymphoma with WT have been reported, most of which were non-Hodgkin lymphomas, and only a few cases were Hodgkin lymphomas. In the present report, we studied a case of diffuse large B cell lymphoma (DLBCL) arising from follicular lymphoma (FL) with WT in the parotid gland and its immunophenotypic and genetic features.

CASE SUMMARY

A 67-year-old man presented with a slowly enlarging right cheek mass for 12 years, and the mass began to change in size over a 2-mo time period. Over time, the patient felt mild local pain and right cheek discomfort. His medical history included a hepatitis B virus infection for 20 years and 30 years of smoking. Gross examination of the excised specimen showed a gray-red and gray-white appearance and a soft texture lobulated external surface neoplasm that measured 9 cm × 8 cm × 7 cm and was well circumscribed by relative normal parotid gland tissue. In cross section, the cut surfaces of the neoplasm were multicystic and had a homogeneous scaly appearance. A small fluid was discovered in the cyst. Bilateral oxyphilic, cuboidal or polygonal epithelium cells and lymphoid intraparenchymal components were observed. Many medium- to large-sized lymphoid cells were observed diffusely in part of the neoplasm, and a few secondary lymphoid follicles were observed at the center or edge of the neoplasm. Immunohistochemical staining showed that the columnar oncocytic cells were positive for AE1/AE3; neoplastic cells located in coarctate follicular were positive for CD20, Pax-5, bcl-2 and bcl-6; and the adjacent diffusely medium- to large-sized lymphoid cells were positive for Pax-5, bcl-6, CD20, MUM-1, bcl-2 and CD79a. The bcl-6 (3q27) break-apart rearrangement was observed, and an Epstein Barr virus test was negative in the tumor cells. The patient survived 6 months after being diagnosed without any treatment.

CONCLUSION

WT-associated lymphoma is a very rare neoplasm in the parotid gland. Most cases are B cell non-Hodgkin lymphomas and involve middle-age and older males. This case highlights the extremely rare association of DLBCL arising from FL with WT and the importance of deliberate evaluation of the WT intraparenchymal stroma. Molecular detection techniques have potential advantages in the diagnosis of lymphoma with WT.

Incidence of Non-Salivary Gland Neoplasms in Patients with Warthin Tumor: A Study of 73 Cases

Warthin tumor is the second most common benign parotid neoplasm. Its association with non-salivary gland neoplasms has been sporadically reported. We reviewed clinical records of Warthin tumor diagnosed on aspiration cytology and surgical pathology to determine if there is any association with other extra-salivary gland malignant neoplasms. Computer search was made for all cases of Warthin tumor diagnosed in the parotid gland by aspiration cytology and surgical pathology at our institution between January 2007 and August 2016. Clinical records of all cases were reviewed for any associated malignant neoplasms and any surgical follow up. All available cytology and histologic material was reviewed. Seventy-three patients (mean 66.9, M:F 1.1:1, age range 43 to 87 years) with Warthin tumor were identified. 45 (62%) were diagnosed on aspiration cytology only, 19 (26%) had cytologic diagnosis as well as concordant surgical follow up, and 9 (12%) were diagnosed based on surgical pathology only. Average age for patients with and without secondary malignancy was 70.5-years, and 63.4-years, respectively (p < 0.05). Average pack years for patients with and without secondary malignancy was 45.4, and 39.8, respectively (p > 0.05). Twenty-seven (37.0%) patients harbored a malignant neoplasm. Association of extra salivary gland malignant neoplasms in 37.0% of our cases suggest that the prevalence of secondary non-salivary neoplasms in patients harboring Warthin tumor might have been underestimated. Squamous cell carcinoma was the most commonly associated non-salivary malignant neoplasm. The association of Warthin tumor with smoking plays an important role in this increased rate of malignancy, and this is supported by the fact that smoking is highly associated with head and neck and lung cancers.

Follicular Lymphoma Diagnosed in Warthin Tumor: A Case Report and Review of the Literature

Warthin tumor is one of the most common benign salivary gland tumors. It is unusual and difficult to diagnose follicular lymphoma within the lymphoid tissue of Warthin tumor. We present a rare case of a 69-year-old man with systemic follicular lymphoma initially diagnosed in a Warthin tumor. Lymphomas occurring within Warthin tumors are rare, however, follicular lymphoma is most commonly reported. Because these patients require further treatment depending on the stage of a disease, it is important for a pathologist to review the histology of Warthin tumors diligently to identify occult lymphomas.

Presentation of Chronic Lymphocytic Leukemia/Small Lymphocytic Lymphoma in a Warthin Tumor: Case Report and Literature Review

Warthin tumor is the second most common salivary gland neoplasm. It occurs more commonly in males than in females. Malignant transformation in Warthin tumor is a rare but well-recognized phenomenon; however, the development or presentation of lymphoma in a Warthin tumor is rare. An 80-year-old man presented with painless mass of the right parotid gland of 2 years duration with recent ulceration of the overlying skin and right cervical lymphadenopathy underwent a surgical resection of parotid mass and biopsy of the periglandular lymph nodes. The histological diagnosis was malignant lymphoma, chronic lymphocytic leukemia/small lymphocytic lymphoma, present within the stroma of a Warthin tumor, and also present within the adjacent lymph node. This case is the third reported case describing a collision of Warthin tumor and chronic lymphocytic leukemia/small lymphocytic lymphoma. It also emphasizes the importance of careful examination of the lymphoid stroma of these tumors.

Nodular Lymphocyte-Predominant Hodgkin Lymphoma in a Warthin Tumor of the Parotid Gland: A Case Report and Literature Review

Hodgkin lymphoma (HL) associated with Warthin tumor (WT) is extremely rare, accounting for only 3 cases of classical HLs. Here, we report for the first time the occurrence of a nodular lymphocyte-predominant Hodgkin lymphoma (NLPHL) involving the lymphoid stroma of a WT of the parotid gland. Pathogenesis of WT is controversial, with both a nodal and a parenchymal possible origin. On the other hand, extranodal involvement by HLs is uncommon. In our case, the coexistence of a WT and of a NLPHL within its stroma and in cervical lymph node emphasizes the importance of a careful evaluation of the lymphoid tissue in WT in order to exclude the possibility of an associated lymphoid malignancy.

An unusual initial presentation of mantle cell lymphoma arising from the lymphoid stroma of warthin tumor

Background

Warthin tumors presenting concomitantly with a lymphoma is vanishingly rare with only 15 reported cases in English literature. Herein, we report an unusual initial presentation of a mantle cell lymphoma involving the lymphoid stroma of a Warthin tumor.

Case presentation

A seventy-seven year old otherwise healthy gentleman with a 50-pack year smoking history presents with a slowly enlarging left cheek mass. CT scan of the neck demonstrated a left parotid gland tumor measuring 3.4 cm in greatest dimension. He underwent a left superficial parotidectomy, with subsequent histopathologic examination revealing a Warthin tumor with extensive expansion of the lymphoid stroma. Flow cytometric, immunohistochemical, and cytogenetic studies of the stromal component of the tumor confirmed the presence of a mantle cell lymphoma. Clinical staging demonstrated stage IVa disease, and was considered to be at low to intermediate risk due to the slow growth of the parotid lesion. The patient is undergoing close follow up with repeat PET-CT scans at six months.

Conclusion

To the best of our knowledge, this is the first well documented collision tumor between mantle cell lymphoma and a Warthin tumor. This case also brings to light the significance of thorough evaluation of the lymphoid component of Warthin tumor.

Primary Merkel cell carcinoma of the parotid gland

Primary Merkel cell carcinoma (MCC) is a neuroendocrine tumor that typically affects older whites. It usually originates in the dermis, but in rare instances it has arisen in other primary sites, including the oral mucosa and the parotid gland. Explanations for the presence of MCC in these atypical locations have included theories of malignant transformation and neuroendocrine migration. We describe the case of a 35-year-old white woman who had an MCC in the parotid gland and no evidence of any other primary cutaneous lesion. A left superficial parotidectomy with facial nerve preservation was performed, and a histologic diagnosis of MCC was made. Positron-emission tomography was negative for other lesions, and postoperative radiation therapy was administered for local control. To the best of our knowledge, this is only the sixth case of a primary MCC of the parotid gland to be reported in the English-language literature; of these 6 patients, ours was by far the youngest. Otolaryngologists should be familiar with this rare but potentially fatal neoplasm.

T cell lymphoblastic lymphoma in parotidectomy for Warthin's tumor: case report and review of the literature

Lymphomas associated with Warthin's tumor (WT) are extremely uncommon and the majorities are of B cell type. We report the simultaneous occurrence of T-cell lymphoblastic lymphoma (T-LBL) and WT in an 81-year-old patient, who presented with fever, night sweats and enlargement of the right parotid gland. The parotidectomy specimen showed a WT with extensive replacement of the lymphoid stroma by T-LBL, but preservation of the oncocytic epithelium. Staging investigations revealed mediastinal and abdominal lymphadenopathy, bilateral pleural effusions and bone marrow infiltration, in keeping with stage IVB disease. The patient received combination chemotherapy treatment but responded poorly, and died three months after diagnosis. To our knowledge, this is the first case report of T-LBL involving WT. The present study indicates that the lymphoid stroma in WT belongs to the systemic lymphoid tissue and can be involved in disseminated lymphoma. It highlights the importance of careful examination of WT's lymphoid stroma for the possible presence of any coexistent malignancy.

Molecular assessment of allelic loss in Warthin tumors

Warthin's tumors are benign lesions of the head and neck that have a characteristic morphologic appearance. The etiology of Warthin's tumors is controversial and whether they are true neoplasms or developmental malformations continues to be debated. In this study, we examined 12 Warthin tumors with a molecular and immunohistochemical approach. Immunostains for p53 and p16ink were performed. The epithelial and lymphoid components of each lesion were microdissected and PCR was performed for 13 microsatellite markers at or near common tumor suppressor genes. The results were analyzed semiquantitatively using capillary electrophoresis. Frequency of allelic loss was calculated. The epithelial component of all tumors was negative for p53 and p16ink. By molecular genotyping there was only one case that had one locus with allelic imbalance, while the remainder had no evidence of clonal allelic loss. The immunohistochemical and molecular results in this study lend support to the hypothesis that Warthin tumors are non-neoplastic, as there was no evidence of aberrant staining for tumor suppressor gene protein products and no evidence of consistent clonal allelic losses.

Initial diagnosis of small lymphocytic lymphoma in parotidectomy for Warthin tumour, a rare collision tumour

Warthin tumours (WT) and malignant lymphomas are only rarely associated, and most are examples of involvement of the lymphoid stroma of WT by a disseminated lymphoma. This report describes a case where excision of a parotid mass led to the initial diagnosis of WT and small lymphocytic lymphoma (SLL). The diagnosis of SLL was confirmed by immunohistochemistry and molecular studies. The patient had stage IV A disease and is currently in chemotherapy induced complete remission. This case highlights the extremely rare association of SLL with WT and the importance of evaluation of the WT stroma, where the pale proliferation centres of SLL may mimic germinal centres of reactive lymphoid nodules.

Warthin's tumour: a study of 78 cases with emphasis on bilaterality, multifocality and association with other malignancies

The authors reviewed the clinical records and the histopathological preparations of 78 cases of Warthin's tumours (WTs), treated at the Department of Dental Sciences, Centre for the Study of Oral Tumours, of the University of Bari. All the surgical specimens had been fixed in neutral buffered formalin, sampled according to the step-serial, whole-specimen sectioning technique, embedded in paraffin and stained with haematoxylin-eosin, periodic acid Schiff and Gomori's reticulin. The results showed that Warthin's tumours characteristically affect the parotid gland, and most frequently arise in adults (mean age=57 years) and in males (95%). Multiple tumours were detected in 16 cases (20.5%), and five of these were bilateral (6.5%). One of the multifocal tumours involved an intra-parotideal lymph node and the laryngeal piriform sinus. In addition, 13 cases (16.6%) were associated with other malignancies. These data indicate that multiple (synchronous or metachronous) WTs may occur more frequently than previously reported. The high rate of multiple WTs detected in the current study may result from extensive and accurate sampling of these neoplasms for histopathological evaluation. Consequently, complete preoperative work-up of patients harbouring parotideal tumours consistent with or suspicious for WT is necessary. The work-up should include CT scans and/or magnetic resonance imaging of both parotid glands, to exclude the occurrence of multiple tumours, which may be clinically undetectable. Also, fine needle aspiration biopsy may be an accurate tool for excluding malignant neoplasms and for better planning subsequent surgical procedures. These usually consist in (bilateral) superficial parotidectomy and should be followed by long term follow up of the patients, in view of possible metachronous WTs, even after prolonged time intervals.

Merkel cell carcinoma of the parotid gland associated with Warthin tumour: report of two cases

AIMS

Two cases of Merkel cell carcinoma occurring simultaneously and in close association with a Warthin tumour of the parotid gland are reported.

METHODS AND RESULTS

The patients were a 65-year-old man and a 70-year-old man, respectively. The Merkel cell carcinoma component was immunoreactive for chromogranin and keratin 20 and contained neuroendocrine-type granules at the ultrastructural level.

CONCLUSIONS

The histogenesis of this heretofore undescribed combination is discussed.

Follicle center lymphoma and Warthin tumor involving the same anatomic site. Report of two cases and review of the literature

We report 2 cases of follicle center non-Hodgkin lymphoma (NHL) and Warthin tumor involving the same site. Case 1 is a 68-year-old woman with Warthin tumor and grade 1 follicular NHL involving a periparotid lymph node. She had localized NHL and was treated with radiation therapy; dissemination developed 54 months later. Case 2 is a 55-year-old man with a 17-year history of a parotid mass with gradual enlargement during the last 5 years. Surgical excision revealed Warthin tumor and grade 1 follicular NHL involving the right parotid gland and surrounding lymph nodes. Immunohistochemical studies supported the diagnosis of NHL in both cases; the neoplasms were positive for CD20 and BCL-2 and negative for CD3. Polymerase chain reaction analysis done on paraffinembedded tissue of case 1 revealed monoclonal immunoglobulin heavy chain gene rearrangement and bcl-2/JH fusion DNA sequences diagnostic of the t(14;18)(q32;q21). The small size of the Warthin tumor in case 1, clearly arising in lymph node, supports the hypothesis that Warthin tumor arises from heterotopic salivary gland ducts within lymph nodes. The localized NHL in both patients suggests that the NHL initially arose in the lymph node involved by Warthin tumor, and, thus, the Warthin tumor may have provided a source of long-term antigenic stimulation from which a monoclonal B-cell population subsequently arose.

Extraparotid Warthin's tumor

Warthin's tumor (papillary cystadenoma lymphomatosum) is a well-known benign tumor of the parotid gland. Extraparotid tumors occasionally arise in the cervical region, where they may well be seen by the dermatologist. The following is a case report of an extraparotid Warthin's tumor encountered in a dermatology practice, with a review of the important clinical and histopathologic features of this tumor.

Molecular characterization of Warthin tumor

OBJECTIVE

Warthin tumor of the salivary gland is composed of oncocytic epithelium with a prominent follicular lymphoid infiltrate. The purpose of this study was to characterize the clonality of this lymphoid component by means of polymerase chain reaction technology.

STUDY DESIGN

DNA was isolated from paraffin-embedded tissue from 20 cases of typical Warthin tumor of the salivary gland and amplified by polymerase chain reaction to assess B- and T-cell clonality.

RESULTS

No dominant clonal populations were identified in any tumor. However, minor clonal expansions of both B and T cells were detected in up to 50% of tumors (immunoglobulin H, 50%; T-cell antigen receptor beta, 10%; T-cell antigen receptor gamma, 5%). No tumors showed evidence of bcl-2 proto-oncogene translocation, whereas 95% contained detectable Epstein-Barr virus DNA.

CONCLUSION

The B- and T-cell components of Warthin tumor are polyclonal with oligoclonal expansion of both T and B cells in some lesions.

Detection of p53 gene abnormality by sequence analysis of archival paraffin tissue. A comparison with fresh-frozen specimens

This parallel study was designed to compare the sensitivity and specificity of detection of point mutations in fresh-frozen and formalin-fixed, paraffin-embedded breast cancer tissue. Sequence analysis of exon 5 of p53 gene was performed on polymerase chain reaction-amplified DNA from 25 infiltrating ductal carcinomas of the breast. Four tumor showed mutations with identical base substitutions in their respective codons of both frozen and paraffin-embedded specimens. We conclude that subtle genetic alterations can be detected in archival paraffin tissue with an accuracy comparable to that of fresh-frozen histologic samples.

Epidermoid carcinoma arising in Warthin's tumour: a case study

We present a case of epidermoid carcinoma arising in Warthin's tumour of parotid gland in an 80-year-old woman. Light microscopy revealed small foci typical of benign Warthin's tumour with transition to epidermoid carcinoma. Immunohistochemical and ultrastructural observations confirmed the epidermoid features of the malignant cells. The differential diagnosis of a metastasis from an epidermoid carcinoma to the stroma of Warthin's tumour and also of the so-called metaplastic variant of Warthin's tumour is discussed.

Molecular biological analysis of paraffin-embedded tissues

Molecular biology techniques have been adapted to the analysis of paraffin-embedded tissues (PETs), expanding their clinical utility. In vitro amplification with the polymerase chain reaction (PCR) promises to be the most useful means of retrospective analysis because it can be performed successfully on nucleic acids that have been partially degraded during fixation, paraffin embedding, and the extraction process. Five clinical situations in which DNA analysis of PETs can be helpful are: (1) confirmatory molecular diagnosis of lymphoma in which fresh tissue has not been obtained at the time of surgery, (2) identification of infectious agents, (3) genetic characterization of a putative inherited disease in which the affected individual has died, (4) confirmation of donor cell malignancy in transplant recipients, and (5) specimen identification. The role of the pathologist in molecular diagnosis will grow because of the feasibility of using PETs, a venue unique to our profession.

Retrospective DNA analysis using fixed tissue specimens

The recent explosion of scientific and technical knowledge in the field of molecular biology has allowed us to make important advances in our understanding of the molecular basis of many human diseases. This technology has now entered the clinical laboratory where identification of specific genetic sequences can aid in the precise diagnosis of hematologic and other malignancies, inherited diseases, specific infectious agents, and inherited predisposition to disease. In addition, it can be applied to prenatal diagnosis, paternity testing, identification of minimal residual disease following treatment, and assessment of drug sensitivity or resistance. In many cases in diagnostic pathology, the need for molecular analysis often is not realized until after a critical tissue specimen has been fixed, embedded, and examined microscopically. Thus, there is a clear need for development of techniques that would allow the retrospective study of archival tissues that have been fixed and embedded in paraffin. This review examines in depth those factors which influence the quality of the DNA available from fixed embedded tissues and discusses the usefulness of polymerase chain reaction amplification in obtaining sufficient diagnostically useful DNA from archival specimens. It is hoped that this review will aid the diagnostic pathologist interested in the application of molecular techniques in the retrospective study of fixed embedded tissues.

Amplification of intermediate-size DNA sequences from formalin and B-5 fixed tissue by polymerase chain reaction

Retrospective analysis of DNA from paraffin-embedded fixed bone marrow biopsy specimens is possible if preceded by amplification of the DNA sequences of interest by the polymerase chain reaction (PCR). These fixed specimens yield degraded DNA that may not be suitable for direct analysis by conventional digestion and hybridization methods. This limitation is circumvented by PCR amplification and subsequent analysis of the amplified products. The model used in this study is the amplification of a 725 base-pair (bp) beta-globin gene sequence encompassing the sickle-cell anemia point mutation, followed by Cvn I digestion. The beta A beta A, beta A beta S, and beta S beta S genotypes are derived from analysis of the allele-specific digestion patterns. Two fixatives were compared: neutral-buffered formalin and a mercury-based fixative (B-5) routinely used for bone marrow biopsies. DNA extracted from B-5-fixed bone marrow specimens was found to be more degraded than DNA from neutral-buffered, formalin-fixed bone marrow aliquots from the same specimens. PCR amplification of the 725 bp beta-globin gene sequence was successful with DNA from formalin-fixed bone marrow specimens, but not with DNA from B-5-fixed identical specimens. Analysis of the amplified product by Cvn I digestion resulted in correct genotype derivation for all patients, normal controls and positive controls (patients diagnosed with sickle-cell anemia or trait). These results indicate that intermediate-size DNA sequences can be amplified and analyzed when DNA is extracted from formalin-fixed bone marrow specimens.(ABSTRACT TRUNCATED AT 250 WORDS)

Polymerase chain reaction: amplification of DNA from fixed tissue

The polymerase chain reaction (PCR) allows the analysis of DNA from biologic samples containing only nanogram quantities of DNA. We used DNA purified from fresh or frozen peripheral blood (PB) leukocytes and formalin, or B-5 fixed bone marrow aspirate clots (BM). A sequence of the beta-globin gene was amplified via the PCR then hybridized with allele specific oligonucleotide probes for hemoglobin A, S, and C. All DNA preparations, including formalin and B-5 fixed BMs, were successfully amplified; the hybridization of the amplified products resulted in patterns consistent with the hemoglobin phenotype for all patients. PCR can be used on DNA from many sources; retrospective studies using paraffin embedded fixed tissue are possible because extremely small amounts of DNA present in fixed tissue can be successfully amplified.

Malignant lymphoma involving a Warthin's tumor: a case with immunophenotypic and gene rearrangement analysis

We describe a Warthin's tumor which was involved by malignant lymphoma. The lymphoma was classified in the Working Formulation as follicular and diffuse, mixed small cleaved and large cell type. Frozen section immunohistochemical studies revealed an abnormal immunophenotype: immunoglobulin-negative and B-lineage. Gene rearrangement analysis confirmed the diagnosis by demonstrating rearrangements of both the immunoglobulin heavy and kappa light chain genes. The bcl-2 gene was also rearranged, consistent with the presence of the t(14;18) (q32;q21) translocation which is typically seen in follicular lymphomas. The T-cell receptor beta chain gene retained the germline configuration. The results in this case highlight an advantage of molecular techniques as compared with immunophenotypic analysis: gene expression is not required to demonstrate clonality.

Warthin's tumor

Warthin's tumor, classed as a monomorphic adenoma, ranks second to pleomorphic adenoma in the incidence of benign neoplasms of the parotid gland. By embryologic and clinicopathologic definitions, it is a neoplasm of the parotid gland and its environs, including parotid lymph nodes. Histopathologic diagnosis requires an oncocytic (mitochondria-rich) epithelium and lymphoid stroma. Malignant Warthin's tumors are rare and are carcinomas arising from the ductal component, or non-Hodgkin's lymphomas arising from the lymphoid tissue.