Paratesticular Mass in an Older Male

Deloar Hossain, M.D.

Specimen Type:

Testis

History:

42 year old male with paratesticular mass.

Pathologic Features:

Gross Description: The orchiectomy specimen shows a well circumscribed, tan gray, firm and nodular paratesticular mass measuring 2.5x 2x 2 cm at the inferior pole of the testis. Cut section shows a fibromuscular, tan white and focally hemorrhagic parenchyma (Fig: 1). The mass abuts and slightly compresses the testis but does not appear to infiltrate the organ.

Microscopic Description:The neoplasm is composed of plump spindle cells with pleomorphic nuclei and tumor giant cells (Fig: 2). There is brisk mitotic activity with rare abnormal mitotic figures are identified (Fig: 3). The tumor focally displays a fascicular arrangement and also necrosis (Fig; 4).

Immunohistochemical stains:

The tumor cells display positive immunoreactivity against the following antibodies:

  • Vimentin (diffuse and strong) (Fig: 5)
  • Smooth muscle actin (focal) (Fig: 6)
  • Muscle specific actin (focal)
  • Calponin (focal)
  • Myo-D1 and myogenin (cytoplasmic staining)

They are non-immunoreactive against the following antibodies:

  • Pancytokeratin
  • High molecular weight keratin 34BE-12
  • CD99
  • Desmin
  • S100
  • CD34
  • Caldesmon
  • CD68

Differential Diagnosis:

The differential diagnoses include a myriad of spindle cell tumors ranging from benign neoplasms to malignant spindle cell tumors of various lineages:

Solitary fibrous tumor: This neoplasm involves the serosal surface and is more common in the pleura. It consists of fusiform cells with indistinct cytoplasmic borders arranged in interlacing fascicles or randomly around an elaborate vasculature. A characteristic feature of this neoplasm is the presence of prominent hyalinization, which is not observed in our case. Immunohistochemistry typically shows expression of CD34 and CD99.

Malignant fibrous histiocytoma: The anaplastic features and presence of tumor giant cells make it difficult to exclude this differential diagnosis. The paucity of inflammatory cells coupled with the positive, albeit focal, immunoreactions for smooth muscle actin, muscle specific actin and myogenin, Myo-D1 suggest a sarcoma of different lineage. CD68 immunoreactivity is equivocal and interpreted as negative in this case.

Pleomorphic carcinoma/Sarcomatoid carcinoma: Sarcomatoid carcinoma has at least focal morphologic features of a mesenchymal neoplasm, but other areas may exhibit obvious epithelial morphology. Immunoreactivity to epithelial markers is evidence of epithelial differentiation, although immunoreactivity to keratins and other epithelial markers are certainly not uncommon in sarcomas and are not themselves diagnostic of sarcomatoid carcinoma. Immunohistochemical stains in this case were negative for pancytokeratin and high molecular weight cytokeratin.

Malignant peripheral nerve sheath tumor: This neoplasm is composed of tapered spindle cells with cigar shape or wavy nucleus arranged in dense or hypodense fascicles. Nuclear palisading, tactoid structures and hyperplastic perivascular change may be observed. Immunohistochemistry is positive for S-100 protein, albeit often focally.

Synovial sarcoma: This neoplasm may occur at any site. It can be monophasic or biphasic with both epithelial and spindle cell components. Tumor giant cells are infrequent. Immunohistochemistry shows positive reactions for pancytokeratin and CD99 (in 60% of cases).

Embryonal rhabdomyosarcoma, spindle cell type: This neoplasm is composed of spindle cells with cigar shape nucleus and prominent nucleolus surrounded by eosinophilic fibrillar cytoplasm with distinct borders. Cytoplasmic striations may be observed. The cells are arranged in fascicles or bundles sometimes simulating leiomyosarcoma. It has a predilection for the paratesticular area. Also referred to as spindle cell rhabdomyosarcoma, the tumor has a more favorable clinical course compared to the usual type of embryonal rhabdomyosarcoma. Immunohistochemistry shows myogenic differentiation with a distinctly nuclear immunoreactivity observed for myogenin as oppose to cytoplasmic.

Leiomyosarcoma: This neoplasm exhibits spindled or fusiform cells with cigar-shape nucleus surrounded by eosinophilic cytoplasm. Muscle striations are absent. Tumor giant cells can be frequent. Inflammatory cells are not a prominent feature. If present, inflammatory cells are usually composed of lymphocytes. Immunohistochemistry shows myogenic differentiation.

Diagnosis:

Spindle Cell Sarcoma, Grade 3 of 3

The results of immunohistochemical studies suggest malignant fibrous histiocytoma.

Positive immunohistochemistry:

  • Vimentin
  • Smooth muscle actin
  • Muscle specific actin
  • Calponin
  • Myo-D1/myogenin

Comment: Soft tissue tumors remain one of the most challenging neoplasms a pathologist face. Immunohistochemistry is widely employed to determine the lineage of poorly differentiated sarcomas. It is advisable to use a panel of antibodies initially rather than isolated ‘confirmatory’ ones when confronted with a neoplasm of uncertain type. The results of immunohistochemical studies need to be interpreted in conjunction with the clinical and histomorphologic findings to avoid misinterpreting false-positive and false-negative results. It is also important to take note of the localization and features of a positive immunoreaction, i.e., whether granular or dot-like, whether the reaction is cytoplasmic, membranous, nuclear or paranuclear, since the differentiation of two closely similar tumor types sometimes hinges on these details.

References:

  1. Weiss SW, Glodblum JR. Soft tissue tumors. 5th ed. 2008.
  2. (2) Cessna MH, Zhou H, Perkins SL, Tripp SR, Layfield L, Daines C, Coffin CM. Are myogenin and myo-D1 expression specific for rhabdomyosarcoma?: A study of 150 cases with emphasis on spindle cell mimics. Am J Surg Path. Sep 2001,25(9),1150-57.
  3. (3) Fletcher CDM, Unni KK, Mertens F (editors). Pathology and Genetics. Tumours of soft tissue and bone. WHO classification of tumours. 2002.