History: A 38 year old woman presented with a several month history of an enlarging painful mass of the right knee. Physical examination showed a firm, tender mass over the medial knee region. An MRI revealed a 6.9 x 4.7 x 3.4 cm, heterogeneously enhancing soft tissue mass with areas of hemorrhage and probable
Grossly, the mass was firm, variegated, white-tan to dark-brown, and well-circumscribed (Fig. 1).
Microscopically, the tumor infiltrated into tendon (Fig. 2). Tumor cells showed a nesting pattern and clear cells with focal pigment (Figs. 3-4). Prominent nucleoli were present (Figs. 5-6). The tumor was positive for a melanoma cocktail (Fig. 7) and S100 (Fig. 8).

Immunohistochemical studies showed the tumor to be positive for S100 and Melanoma cocktail, but were negative for synaptophysin and NFP. FISH was performed and showed 97% tumor cells were positive for fusion transcript of EWSR1(22q12) and ATF1 (12q13.13) loci.

Diagnosis: Clear Cell Sarcoma of Soft Parts

Huina Zhang, M.D., Ph.D., Ravi Raghavan, M.D.
and Donald R. Chase, M.D.
Department of Pathology & Human Anatomy
Loma Linda University Medical center, Loma Linda, California

Discussion: Clear cell sarcoma (CCS) is a rare soft tissue sarcoma with melanocytic differentiation, which is also known as malignant melanoma of soft parts. Although it has certain morphologic similarities to malignant melanoma, CCS is a clinicopathologically and genetically distinct from the conventional malignant melanoma. It mainly affects young adults between the ages of 10 to 40 years with a median age of approximately 30 years. CCS typically presents as a slowly growing, firm, deep-seated nodule in the distal extremities, most often located around the ankle or foot, followed by the knee, wrist, and hands. It is usually associated with tendons, tendon sheaths, or aponeuroses, with rare involvement of the subcutaneous tissue or dermis. CCS usually follows a protracted clinical course, with frequent local recurrences and late metastases to regional lymph nodes, lungs, and bone. The long-term prognosis of CCS is poor and one study showed the survival rates at 5, 10, and 20 years were 67%, 33% and 10%, respectively. Early diagnosis and initial wide excision are essential for local control and a more favorable outcome. Unfavorable prognostic factors include large tumor size (>5 cm), presence of necrosis, early local recurrence, and positive resection margins.
Grossly, CCS is usually a lobulated or multi-nodular, firm, tan-grey mass and the size ranges from 0.4 cm up to 14.5 cm in greatest diameter. It may show infiltration into the tendons and aponeuroses. The cut surface may show focal haemorrhage, necrosis or cystic changes and often is gritty.
Microscopically, CCS is highly infiltrative and is characterized by a nested, bundled or fascicular growth of uniform fusiform or spindled-to-epithelioid cells, separated by prominent fine collagenous framework of various thicknesses. The tumor cells contain abundant clear or pale eosinophilic cytoplasm and centrally located, round to ovoid vesicular nuclei with prominent basophilic nucleoli. Scattered multinucleated giant cells with 10 to 15 peripherally distributed nuclei in a wreathlike pattern are commonly present. In about half to two thirds of cases finely granular melanin pigment may be identified. The stroma may be barely visible, fibrotic or hyalinized. Focal areas of necrosis may be also noted. The mitotic rate is usually low, and pleomorphism is absent.

Immunohistochemical studies of CCS reveal that the tumor cells express antigens associated with melanin synthesis including diffuse immunoreactivity with HMB-45, nuclear and cytoplasmic immunoreactivity to S-100 protein, and reactivity with the microphthalmia transcription factor (MITF). There may be focally reactivity with Melan-A, neuron-specific enolase and vimentin, but the tumor is typically negative for EMA, keratins, and desmin.

Genetically, CCS has a distinct genetic background including a reciprocal chromosome translocation t(12;22)(q13;q12), which can be detected by conventional chromosomal analysis, FISH or reverse transcriptase polymerase chain reaction in 70-90% of CCS. This translocation results in fusion of the 3’ portion of the Ewing sarcoma (EWSR1) oncogene on chromosome 22q12 with the 3’ portion of the activating transcription factor 1 (ATF1) oncogene on chromosome 12q13, giving rise to the EWSR1/ATF1 chimeric transcript. EWSR1/ATF1 functions as a transcriptional regulator that induces the expression of MITF in CCS and plays a crucial role in melanocytic differentiation and growth or survival of tumor cells.

Differential Diagnoses:

• Metastatic melanoma is the most important mimic of CCS in the soft tissue and can be extremely difficult to distinguish from CCS because the significant overlapping features at morphologic, immunophenotypic and ultrastructural levels. The clinical context including a deep-seated infiltrative mass in the distal extremities, no proceeding history of cutaneous, mucosal or ocular tumor, the absence of junctional activity, and the uniform cytomorphology are helpful clues to the diagnosis of CCS, but in some cases detection of the translocation or its gene product is needed.

• Paraganglioma-like dermal melanocytic tumor is a recent-described, rare, benign neoplasm derived from melanocytes. It is primarily a non-pigmented, well-demarcated skin nodule at the extremities, most common in adult females. It is composed of clear to amphophilic epithelioid cells in an organoid or nest-like pattern separated by delicate fibrous strands and blood vessels, which is a reminiscent of those of paraganglioma. The tumor cells may also express S-100 protein, Melan-A, HMB-45, and microphthalmia transcription factor but lacks pancytokeratin or smooth muscle actin. FISH analysis of 5 cases revealed an intact EWS gene locus, supporting absence of the clear cell sarcoma 12;22 translocation.

• Malignant peripheral nerve sheath tumor (MPNST) is usually associated with a large peripheral nerve, and usually has manifestations of neurofibromatosis. It has significant myxoid stroma, long fascicles of spindle cells with slender, tapering or wavy nuclei and indistinct cytoplasm. Although it expresses S-100 protein, MPNST is negative for HMB-45 and Melan-A.

Summary: CCS is an extremely rare soft tissue malignancy with melanocytic differentiation, which is characterized by nests and short fascicles of uniform spindled-to-epithelioid cells with pale, eosinophilic cytoplasm and prominent nucleoli, separated by dense fibrous septa. Immunohistochemically, expression of HMB-45 is usually stronger and more diffuse than S-100 protein. Furthermore, t(12;22) translocation with EWSR1-ATF1 fusion is a typical genetic feature in CCS.

Suggested Reading:

Hornick JL. Practical Soft Tissue Pathology: A Diagnostic Approach. Elsevier.
Dim DC, Cooley LD, Miranda RN. Clear cell sarcoma of tendons and aponeuroses: a review. Arch Pathol Lab Med. 2007, 131(1):152-6.
Deyrup AT1, Althof P, Zhou M, Morgan M, Solomon AR, Bridge JA, Weiss SW. Paraganglioma-like dermal melanocytic tumor: a unique entity distinct from cellular blue nevus, clear cell sarcoma, and cutaneous melanoma. Am J Surg Pathol. 2004, 28(12):1579-86.
Goldblum JR, Folpe AL and Weiss SW. Enzinger & Weiss’s Soft Tissue Tumors: 6th ed. Elsevier.

History:  A 21 year old man presented with an 11 month history of a slow growing, painless subcutaneous mass in the left inguinal area. A pelvic X-ray showed a 7 x 4 x 2.8 cm well circumscribed periarticular calcified mass within the soft tissue of the hip. It consisted of multiple small calcified nodules. Serum calcium, phosphate and alkaline phosphatase levels were normal.
The mass was composed of white, granular material surrounded by a fibrous tissue capsule. The cut surface was hard, calcified, light tan and chalky. Microscopically, it showed multiple, solitary and confluent nodules of calcification in a matrix of granular debris (Figs. 1, 2, 3, 4 ). Associated were histiocytes, multinucleated giant cells and fibroblasts (Figs. 5, 6).

“August 2014: A 21 year old man with a mass in the inguinal region”Continue reading

History:A 69 year-old woman from Laos presented with hemoptysis and a 9 cm mass in the right middle and lower lung lobes (Fig. 1). It obliterated the right middle lobe bronchus, obstructed the inferior pulmonary vena cava and extended to the chest wall. Ten years prior, the tumor was recognized by CT scan, but therapy had not been given. Metastatic workup at the current presentation failed to show a different site of origin. “July 2014: A large lung mass in a 69 year old woman from South Asia”Continue reading

History: A 58 year-old woman with a 6 year history of dermatomyositis presented with a 7 month history of a painless 1.5 x 1.0 cm skin ulcer near her right elbow on the dorsal surface of the proximal forearm. She had a 6 year history of methotrexate (MTX) treatment during which time other cutaneous wounds had arisen, but unlike this one, had healed. Physical examination also showed decreased muscle strength in her shoulder and hip flexors, but neither lymphadenopathy nor hepatosplenomegaly were identified.

Microscopically the mass was centered in the dermis (Figs. 1,2) and consisted of hypercellular, sheet-like dermal infiltrates (Figs. 3,4). The infiltrate was particularly noteworthy for scattered atypical cells with large bi- or mono-lobed nuclei. These cells also had pale vesicular chromatin, amphophilic cytoplasm and were felt to be Reed-Sternberg (RS) cells and variants (Figs. 5,6). Admixed with them were small lymphocytes, plasma cells, neutrophils and rare eosinophils. The RS cells and variants stained positive for CD15, CD30, and PAX-5, but negative for CD3, CD20 and CD45 (Fig. 7). An Epstein-Barr virus (EBV) staining by EBER in-situ hybridization was positive in the RS cells/variants (Figs. 8).

After withdrawing MTX therapy the site healed well, and the patient was spared additional chemotherapy and radiation. However after 13 months the tumor recurred locally at the same location.

Diagnosis: Primary Cutaneous Hodgkin Lymphoma Presenting as an Epstein-Barr Virus Positive Methotrexate-associated Lymphoproliferative Disorder

Ying Zhao, MD; Ravi Raghavan, MD; Jun Wang, MD; Donald R Chase, MD
Department of Pathology and Human Anatomy,
Loma Linda University Medical Center, Loma Linda, California
California Tumor Tissue Registry, Loma Linda, California

Discussion:
There are only a few reported cases of Hodgkin lymphoma (HL) presenting as a primary cutaneous lesion (Mukesh et al). Patients are usually in the terminal phase of the disease and have already sustained extensive systemic and lymph node involvement.

According to the 2008 WHO classification of tumors of hematopoietic and lymphoid origin, our case presentation tumor falls into an iatrogenic subgroup of immunodeficiency-associated lymphoproliferative disorders (LPD). In fact, MTX was the first reported agent associated with LPD, noticed when it occurred in patients being treated for rheumatoid arthritis (RA). The frequency of this relationship is not well known. In one large survey, 478 lymphoma cases were recorded among 101,589 patients treated with methotrexate and/or anti-TNF therapy for RA (Wolfe et al.). Among the MTX-LPD, 40-50% were extranodal, including gastrointestinal tract, skin, liver, spleen, lung, kidney, thyroid gland, bone marrow and soft tissue (Hoshida et al). According to the WHO classification, MTX-LPD mainly consists of diffuse large B-cell lymphoma (35-60%) and classical Hodgkin lymphoma (12-25%). Overall, 40% MTX-LPD were EBV positive, with EBV detected more frequently in Hodgkin lymphoma (~80%) than in DLBCL (~25%) or other B-cell lymphoma types. The hypothesis of pathogenesis of MTX-LPD is that the immunosuppressive state induced by MTX administration might contribute to development of LPD. It’s also noteworthy that patients with RA may have a T-lymphocyte defect that allows EBV-infected B-lymphocytes to survive.

In this case report, the tumor cell morphology and immunophenotype demonstrate classical Hodgkin lymphoma, which is associated with MTX treatment for the dermatomyositis and has EBV positivity. The differential diagnosis mainly includes cutaneous CD30+ lymphoproliferative disorders as listed below:

• Hodgkin lymphoma-like post-transplantation lymphoproliferative disorder (PTLD), is mainly seen in immunosuppressed recipients following solid organ or bone marrow transplantation. HL-like PTLD cases are almost always positive for EBV, with the EBER present not only in the large atypical cells but also in a substantial subset of the associated bystander small lymphocytes (Wang et al). HL-like PTLD may be either nodal or extranodal. The large atypical RS-like cells express CD45 and B-cell markers (CD20 and/or CD79a) with variable expression of CD30 but not CD15. This entity shows an aggressive clinical course.

• Primary cutaneous anaplastic large cell lymphoma, is a CD30+ T-cell lymphoma presenting with skin nodules or ulceration with diffuse, non-epidermotropic infiltrates. The large CD30+ anaplastic tumor cells have the characteristic morphology of anaplastic cells, showing round, oval or irregularly-shaped nuclei, prominent eosinophilic nucleoli and abundant cytoplasm. The neoplastic cells express T-cell markers such as CD3, CD4, granzymeB and TIA, but are negative for CD15 and EBV.

• Mycosis fungoides with large cell transformation, is a tumor stage of MF and defined by presence of over 25% large lymphoid cells in the dermal infiltrates. With progression, the dermal infiltrates become more diffuse and epidermotropism may be lost. The large CD30+ transformed cells present as large cribriform cells or blast cells with prominent nucleoli. They generally express a T-cell phenotype as CD2+, CD3+, CD4+, but CD15 -.

• Lymphomatoid papulosis is a chronic, recurrent, self-healing papular or nodular skin lesion. The atypical cells can present as anaplastic, immunoblastic or Hodgkin-like cells, which are CD30+, CD15-, CD4+, and CD20- . Although this CD30 positive T-cell lymphoproliferative disorder has a malignant morphology, it is self-healing.

Spontaneous complete remission after cessation of MTX has been reported in DLBCL (up to 40%) and classical Hodgkin lymphoma (up to 30%) (Hoshida et al., Rita Rizzi et al.). The majority of responses occurred in EBV-positive cases and remission generally occurred within 4 weeks. In our case, despite positive margins, the patient went into remission for 13 months. Its recurrence, however, suggests the advisability to continue to monitor the patient for many months. Little is known about the interval for the recurrent tumor after initial spontaneous remission. It will be important to accumulate and evaluate many more cases of MTX-LPD and examine their clinical correlates.

Suggested Reading:
Mukesh M et al, Primary cutaneous Hodgkin’s lymphoma. Clin Exp Dermatol. 2009 Dec;34(8):e673-5.
Hoshida et al, Lymphoproliferative disorders in rheumatoid arthritis: Clinicopathological analysis of 76 cases in relation to methotrexate medication. .J Rheumatol. 2007 Feb;34(2):322-31.
Rita Rizzi et al, Spontaneous remission of ‘‘methotrexate-associated lymphoproliferative disorders’’ after discontinuation of immunosuppressive treatment for autoimmune disease.Review of the literature. Med Oncol (2009) 26:1–9.
Jun Wang et al. Hodgkin lymphoma-like post-transplantation lymphoproliferative disorder. Arch Pathol Lab Med. Vol130: 559-560
Wolfe F et al. The effect of methotrexate and anti-tumor necrosis factor therapy on the risk of lymphoma in rheumatoid arthritis in 19,562 patients during 89,710 person-years of observation. Arthritis Rheum 56:1433-1439.
Takemori N et al. Complete Remission of Methotrexate-Related Epstein-Barr-Virus-Associated Hodgkin-Like Lymphoma following Withdrawal of MTX Coupled with Clarithromycin Administration. Case Rep Hematol. 2012: 658745.
Satoh K et al. Reversible methotrexate-associated lymphoproliferative disorder resembling advanced gastric cancer in a patient with rheumatoid arthritis. Am K Med Sci. 2009 Oct: 338(4): 334-5.

History: A 77-year-old man was found to have a 3.5 x 3.0 x 2.0 cm anterior mediastinal mass. At surgery it was smooth and well-circumscribed. The cut surface was pale tan and lobulated.

Microscopically, the tumor was encapsulated (Fig. 1) and focally cystic (Fig. 2), mostly consisting of small round to oval lymphocytes (Fig. 3). A prominent spindled component was also present (Fig. 4. Generally the cells had scant cytoplasm and stippled nuclear chromatin. Nucleoli were absent or inconspicuous (Fig. 5). By immunohistochemistry, most of the cells marked as immature T-lymphocytes.

Diagnosis: Spindle cell thymoma (WHO type A)

Summer Blount MD, Donald R. Chase MD
Department of Pathology and Human Anatomy,
Loma Linda University Medical Center, Loma Linda, California
California Tumor Tissue Registry, Loma Linda, California

Discussion: “Thymoma” generically describes a tumor of the thymus, irrespective of the cell of origin or degree of malignancy. Throughout the years, knowledge of thymic epithelial cells and lymphocytes has advanced, resulting in several classification schemes. Today thymoma is defined as a benign or low-grade malignant tumor of thymic epithelium with characteristic histologic features, frequently associated with a variable population of immature, but non-neoplastic lymphocytes. So-called “thymic carcinoma” is separated out as a different entity due to differences in both morphology and behavior.

Thymoma is the most common neoplasm of the anterior mediastinum. It occurs in all ethnic groups, ages and sex with no particular predilection. Some thymomas occur in children, but they are more frequently seen in adults, particularly during the fifth and sixth decades of life. The majority is found in the normal thymic location, but due to variations in embryonic descent, the tumor locations may range from the submandibular region to the diaphragm. Symptoms of a thymoma are usually vague but may include dysphagia, hoarseness, chest pain, superior vena cava syndrome, or pleural effusion. There is a fairly common association with myasthenia gravis, as well as a less common association with pure red cell hypoplasia and hypogammaglobulinemia.

Microscopically thymomas are usually at least partially encapsulated by dense fibrous connective tissue. The lobules of thymoma vary widely in size and shape and generally have distinct, but irregular boarders. The formation of perivascular spaces is a characteristic feature seen in approximately two thirds of thymomas. These spaces may contain mature T- and B-lymphocytes, plasma cells and/or mast cells; the center vessel often harbors foamy macrophages and has a tendency to hyalinize.

Imaging, including plain radiographs and computerized tomography (CT), may be helpful in the diagnosis of thymomas. The tumor may be homogeneous or have cystic changes with or without calcifications. CT scans are useful in assessing involvement of surrounding structures. These findings, however, are not specific for thymoma, and may be seen in a variety of other mediastinal tumors including: germ cell tumors, carcinoid tumor and malignant lymphoma.

Thymomas have a morphologic spectrum ranging from tumors consisting almost entirely of lymphocytes to tumors having diffuse growth of atypical polygonal epithelial cells or short spindled epithelial cells. The WHO summarizes this spectrum as follows:

Type A, also known as “spindle cell” or “medullary thymoma” is composed of neoplastic thymic cells having a spindled to ovoid shape without nuclear atypia. These cells may be densely packed in fibroblast-like bundles having a storiform pattern or are loosely organized in ill-defined arrangements. Few or no lymphocytes are present in the background. This subset of thymoma can form a variety of histologic structures including a hemangiopericytoma-like pattern due to dilated sinusoidal vasculature, rosettes, or small glandular spaces that harbors eosinophilic material in the lumen. Additionally the Type A thymoma may have scattered cystic to pseudoglandular spaces with rare glomeruloid structures.

Type AB or “mixed thymoma” is composed of a variable mixture of lymphocyte-poor and lymphocyte-rich thymoma types. In addition to lymphocytes there are small round to spindled epithelial cells with dispersed chromatin and inconspicuous nucleoli. There are no defined criteria as to how much of the two components need to be present in order to diagnosis Type AB thymoma.

Type B1 or “lymphocyte-rich thymoma”, sometimes also referred to as “predominately cortical” or “organoid”, resembles the normal functional thymus. It is composed of sheets of mature lymphocytes resembling thymic cortex with epithelial cells scattered in areas of immature lymphocytes and areas of medullary differentiation. Hassall’s corpuscles may or may not be present.

Type B2 or “cortical thymoma” is composed mostly of large polygonal cells with vesicular nuclei and prominent nucleoli that resemble normal thymic epithelium. The tumor cells are arranged loosely with numerous intermixed immature T-lymphocytes. Commonly, perivascular arrangement of the tumor cells results in a palisaded appearance. This tumor is sometimes also referred to as a “mixed lymphocytic and epithelial thymoma without medullary differentiation”.

Type B3 thymoma may also be referred to as: “epithelial”, “atypical”, “squamoid”, or “well-differentiated thymic carcinoma”. The predominant composition is of medium-sized round to polygonal epithelial cells having mild nuclear atypia. The epithelial cells are mixed with a minor component of intraepithelial lymphocytes, resulting in sheet-like growth.

Not discussed here are rarer subtypes of thymoma referred to as “metaplastic”, “microscopic”, “sclerosing”, or “lipofibroadenomatous” variants.

Suggested Reading:
Shimosato Y, Mukai K, Matsuno Y. AFIP Tumors of the Mediastinum. Series 4. Vol 11. Maryland: ARP Press, 2010: 19-108
Diagnosis and subclassification of thymoma by minimally invasive fine needle aspiration directed by endobronchial ultrasound: a review and discussion of four cases. Moonim MT, Breen R, Gill-Barman B, Santis, G. Cytopathol, Aug 01, 2012; Vol. 23, No. 4, p. 220-228

Molecular Analysis of Thymoma. Badve S, Goswami C, Gökmen-Polar, Y, Nelson Jr. RP, Henley J, Miller N, Zaheer, Narjis A; Sledge Jr. GW, Lang L, Kesle KA, Loehrer Sr. PJ, van Diest P. PLoS ONE, Aug 01, 2012; Vol. 7, No. 8, p. 1-8

Cytokeratin profiles of the thymus and thymomas: histogenetic correlations and proposal for a histological classification of thymomas. Kuo K. Histopathol, May 01, 2000; Vol. 36, No. 5, p. 403-414

Invasive Spindle Cell Thymomas (WHO Type A). Moran CA, Kalhor N, Suster S. Am J Clin Pathol, Nov 01, 2010; Vol. 134, No. 5, p. 793-798

Thymoma: Current Concepts. Kalhor N, Moran CA. Oncology (08909091), Oct 01, 2012; Vol. 26, No. 10, p. 975-981

Tumours and tumour-like conditions of the thymus other than thymoma; a practical approach. den Bakker MA, Oosterhuis, JW. Histopathol, Jan 01, 2009; Vol. 54, No. 1, p. 69-89