The tumor occupies the entire testis and touches but does not invade into tunica albuginea (Fig. 1). Scattered residual seminiferous tubules can be seen within the tumor (Fig. 2). The tumor consists of dense small round cells in a diffuse pattern (Fig. 3). Cells have eccentric nuclei with cartwheel chromatin and scant to moderate amounts of eosinophic cytoplasm (Fig. 4). Tumor cells are invading into tubules (Fig. 5). CD20 reveals membranous positivity (Fig. 6).

• Plasmacytoma
• Lymphoplasmacytoid lymphoma
• Granulocytic sarcoma (chloroma)

Plasmacytoma: A primary testicular plasmacytoma is an extremely rare tumor with about 20 cases published up to date. More often, testicular plasmacytoma represents testicular involvement of multiple myeloma and usually is not detected until autopsy. Grossly, it is firm to soft, tan to gray white that often replaces most of the testicular parenchyma. Microscopically, there is typically a central area of effacement of the underlying testicular tubules and a peripheral zone with intertubular growth of the neoplastic cells. The prognosis of primary plasmacytoma of the testis seems to be good. Nevertheless, a follow-up of some years is necessary to detect possible intramedullar manifestations.

Lymphoplasmacytoid lymphoma (Waldenström macroglobulinmia): This is a rare disease (1.5% of nodal lymphoma) that occurs in older adults. Tumor infiltrates commonly involve the bone marrow, lymph nodes and spleen. Extranodal infiltrates may involve lung, GI tract and skin; testicular involvement has not been reported. Microscopically, the neoplastic cells are small lymphocytes, plasmacytoid lymphocytes and plasma cells. The clinical course is typically indolent, with median survival averaging 5 years.

Granulocytic Sarcoma: The testis is involved on microscopic examination at autopsy in 64% of patient with acute leukemia. Testicular swelling is evident during life in only 5% of patients with leukemia, and testicular enlargement as the presenting manifestation of the disease is exceptionally rare with less than 5 cases reported. Microscopically, because of a prominent component of myelocytes, with round, eccentric nuclei and moderately abundant cytoplasm, and because of an associated chronic inflammatory cell infiltrate that contains mature plasma cells, the tumors are apt to be misinterpreted as plasmacytoma, which may result in a significant error in management. Thus, the diagnosis should at least be thought of any time the diagnosis of plasmacytoma of the testis is being considered. Special stain and immunostain are helpful in making the diagnosis. The tumor is positive for chloroacetate esterase stain and immunohistochemical staining reveals expression of myeloperoxidase, lysozyme, LCA, and CD43.

Primary plasmacytoma of the testis.

• Grossly: the testis is mostly replaced by a firm tumor; the tumor is confined to the testis and extratesticular spread is rarely seen.
• Microscopically:
  1. Diffuse pattern
  2. Plasma cells are predominant, with eccentric nuclei and cartwheel chromatin; scattered anaplastic or bizarre cells may be present.
• Immunohistochemically: positive for immunoglobulin of IgG or IgA; usually negative for B (CD20) and T (CD3) cell specific antigens. EMA may be positive.

Comment: Primary plasmacytoma of the testis is an extremely rare tumor and shows progression to typical multiple myeloma after orchiectomy in most cases (reference 1). Only few cases of synchronous bilateral involvement of the testes have been reported, usually occurring after the onset of multiple myeloma. If a diagnosis of primary plasmacytoma of the testis is rendered, a clinical follow-up of some years is necessary to detect possible intramedullar manifestations. For differential diagnosis, seminoma, granulocytic sarcoma, and lymphoma should be always born in mind whenever a diagnosis of plasmacytoma is being considered. Appropriate stains are needed to make this distinction.

1. Castagna M, Gaeta P, et al. Bilateral synchronous testicular involvement in multiple myeloma. Case report and review of the literature. Tumori. 1997 Jul-Aug;83(4):768-71.
2. Fonseca R, Habermann TM, et al. Testicular lymphoma is associated with a high incidence of extranodal recurrence. Cancer. 2000 Jan 1;88(1):154-61.
3. Ferry JA, Srigley JR, Young RH. Granulocytic sarcoma of the testis: a report of two cases of a neoplasm prone to misinterpretation. Mod Pathol. 1997 Apr;10(4):320-5.