Primary Diffuse Large B-Cell Lymphoma of the Testis

Primary DLBCL of the testis arises in the testis and is associated neither with lymphoma elsewhere nor with leukemia. Involvement of the testis by systemic lymphoma/leukemia defines secondary testicular lymphoma. Primary DLBCL of the testis usually presents in adult patients with a median age in the sixth decade. The most common clinical presentation is a unilateral painless enlargement of the testis, with rapid progression. The history of testicular swelling is generally of weeks' to months' duration, but it may be present for several years.1 In addition to the enlargement of the testis, systemic symptoms such as fever, anorexia, night sweats, and weight loss may be presenting manifestations, and are usually present in 25% to 41% of patients.1,8,9 Involvement of the scrotum and regional retroperitoneal lymph nodes often develops in the course of the disease. Locally there may be a spread to the epididymis, spermatic cord, and scrotal skin, sometimes with sharp scrotal pain.9 

Hydrocele may be present in up to 40% of patients with primary DLBCL of the testis.1 Physical examination usually reveals a unilateral firm mass. Diffuse large B-cell lymphoma of the testis has the tendency for bilateral involvement and is the most common bilateral testicular tumor.10 Subsequent involvement of the opposite testicle with lymphoma may occur months to years after orchiectomy and may be of different histologic subtype; thus, a second tumor may represent another primary rather than disseminated disease.10 However, this is purely speculative as there has not been any documented molecular analysis to support it. Ultrasonography shows a focal hypoechoic mass without a definable capsule or diffuse enlargement and decreased echogenicity of the entire testis that contrasts with hyperechoic areas of normal testis.8 Alternatively, it may appear with diffuse enlargement and generalized hypoechogenicity that contrasts with the normal contralateral testis.8 

Full staging at this time is largely based on the Ann Arbor staging system (I through IV) as it is incorporated into the American Joint Committee on Cancer (AJCC) Cancer Staging Manual, 7th edition.11 In particular, special attention should be paid to the predilection areas for dissemination. Testicular DLBCL shows a specific pattern of dissemination to certain extranodal sites, which include the contralateral testis, the Waldeyer ring, the skin, the lung, and the central nervous system.9,12–14 Serum lactate dehydrogenase levels may be helpful in assessing the tumor volume as well as following the response to therapy. Serum lactate dehydrogenase levels have been correlated with tumor aggressiveness, whereas other tumor markers such as serum beta human chorionic gonadotropin and serum α-fetoprotein are rarely elevated.9 

Tumors vary in size, but are frequently quite large. The median diameter is approximately 6 cm. The cut surface of the orchiectomy specimen reveals a fleshy to firm, often lobulated mass, and the color has been variably described as cream, tan, pale yellow, or slightly pink.15 The majority of the tumors have a homogenous texture and diffusely replace the testis, although multinodular appearance and a discrete solitary intratesticular growth have been noted. Foci of hemorrhage and necrosis may be seen. The tumor may extend into the epididymis, spermatic cord, or adjacent soft tissues, and this may be evident grossly.10,16 

In general the tumor consists of sheets of discohesive cells that diffusely infiltrate. Tumor cells often penetrate diffusely into tissue spaces, producing wide separation of the normal structures, but usually without complete destruction of the basic architecture (Figure 1, A). The seminiferous tubules may be preserved, atrophic, or completely obliterated. Spermatogenic arrest, interstitial fibrosis, and tubular hyalinization are commonly seen. The lymphoma cells frequently also penetrate the reticulin fibers surrounding the tubules, producing a loose, open network of peritubular fibers. In some cases there is destruction of the tubular walls with invasion of the lumen.16,17 The tumor cells are usually medium-sized to large lymphoid cells with oval to round, vesicular nuclei with fine chromatin. There are multiple small, membrane-bound nucleoli. The cytoplasm is usually scanty and amphophilic to basophilic (Figure 1, B). The tumor may show areas that consist of larger cells, with more cytoplasm, that in some cases appear cohesive. These larger cells may possess distinct nucleoli, thus mimicking undifferentiated carcinoma.3 Tumors express various pan B-cell markers such as CD19, CD20 (Figure 2, A), CD22, and CD79a, but may lack one or more of these.3 Cytoplasmic immunoglobulin can be demonstrated in 50% to 75% of cases. The presence of cytoplasmic immunoglobulin does not correlate with the expression of plasma cell markers such as CD38 and CD138, as both markers are rarely coexpressed in the CD20-positive cells.3,18 The tumor cells express CD5 in about 10% of the cases.19 These CD5-positive tumors can be distinguished from the blastoid variant of mantle cell lymphoma by the absence of cyclin D1 expression. CD10 expression is found in 30% to 60% of cases. There is expression of transitional marker MUM-1 in 35% to 65% of cases (Figure 2, B). Nuclear expression of BCL6 has also been described in 60% to 90% of cases.20–21 The proliferative index as detected by Ki-67 staining is high (usually more than 40%)22 (Figure 2, C). Flow cytometry and gene rearrangement/translocation studies are helpful; however, flow cytometry may be difficult, resulting in false negatives using this technique. Using gene expression arrays, DLBCL has been further subclassified into germinal center B-cell–like DLBCL and nongerminal center B-cell–like DLBCL (which includes activated B-cell–like DLBCL and type 3 DLBCL). It is possible to use CD10, BCL6, and MUM-1 to make these distinctions, which may be useful for estimating prognosis.23,24 Al-Abbadi et al24 found that 89% of primary testicular DLBCL belonged to the nongerminal center B-cell–like subgroup and all exhibited high proliferative activity.

The use of cytogenetics, fluorescence in situ hybridization, and array comparative genomic hybridization has shown that genetic alterations in DLBCL of the testis often comprise complex abnormalities, including translocations, trisomies, amplifications, and deletions. The more commonly observed abnormalities include 3q27 abnormalities and 6q deletions. Although deletion of 6q is considered a secondary chromosomal abnormality, in some cases a primary pathologic role is suggested by the observation that it occurs as the sole cytogenetic abnormality.25 Several studies have shown that 6q deletions are more frequent in tumors with an activated B-cell type gene expression profile than in those with a germinal center–cell type of gene expression profile.26,27 Structural alterations of BCL2 oncogene have been detected in DLBCL in general. There is almost no correlation between BCL2 rearrangement and BCL2 protein expression in DLBCL, as almost half of DLBCL cases with BCL2 rearrangement have no or weak BCL2 protein expression, and in reverse, approximately 40% of DLBCL cases with high BCL2 protein expression lack detectable rearrangement. This discrepancy can be explained by mutations in the open reading frame of the translocated BCL2 gene.28,29 However, little is known about the specific frequency of this translocation in DLBCL of the testis.

Treatment can be divided into limited disease (stage I/II) and advanced disease (stage III/IV). For limited disease, standard treatment has not yet been established. Orchiectomy not only provides histologic tissue for diagnosis but also removes a potential sanctuary site, as the blood-testis barrier makes testicular tumors inaccessible to systemic therapy.8 The cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) regimen has been the mainstay of therapy for several decades. In attempts to improve outcome with more intensive chemotherapy, cyclophosphamide, doxorubicin, vincristine, and prednisone–like regimens, such as methotrexate, doxorubicin, cyclophosphamide, vincristine, bleomycin and prednisone and vindesine, doxorubicin, cyclophosphamide, and prednisone MACOP-B, have been used30,31 but they have failed to show additional benefit. More recently, the addition of the chimeric anti-CD20 monoclonal antibody rituximab to the cyclophosphamide, doxorubicin, vincristine, and prednisone regimen (R-CHOP) has led to a marked improvement in progression-free and overall survival.32 Central nervous system relapse remains a major problem; hence, routine central nervous system prophylaxis is recommended. However, the best way to achieve this is still a matter of debate, as central nervous system relapses occur more frequently in brain parenchyma than in meninges, and also in patients who had received intrathecal chemotherapy.8,14 Radiation therapy can be used as a prophylactic therapy to prevent relapse either in the regional lymph nodes or in the contralateral testis, or to treat lymphomatous lesions such as retroperitoneal lymph nodes.8 

For advanced disease, patients should be treated according to the guidelines for the treatment of advanced-stage nodal DLBCL. The standard therapeutic option for patients with stage III/IV disease is conventional anthracycline-containing chemotherapy plus rituximab with the addition of prophylactic scrotal radiotherapy and intrathecal chemotherapy.8 

The standard therapeutic option for patients with relapsed disease has not yet been defined in prospective trials. However, therapeutic strategy should be the same as for other relapsed aggressive non-Hodgkin lymphoma. Therapeutic decision is influenced by age, performance status, and previous treatments.8 

Primary testicular DLBCL is a very aggressive malignancy with a poor outcome. In spite of initial complete remission, most patients even with stage I/II disease experience relapse.8 Most relapses occur within the first 2 years of follow-up. In the largest reported series of patients, the International Extranodal Lymphoma Study Group observed 5- and 10-year overall survival rates of 48% and 27%, respectively.14 Several variables that have been reported as prognostic factors include age, performance status, systemic symptoms, tumor burden >9 cm, spermatic cord involvement, lactate dehydrogenase serum level, histologic grade, vascular invasion, degree of sclerosis, and stage of disease.1,33 

Differential diagnosis of primary testicular DLBCL includes the germ cell tumors such as classic seminoma, spermatic seminoma, and embryonal carcinoma. Granulomatous and viral orchitis may also mimic lymphoma histologically. In general lymphomas occur in an older age group than do typical seminomas. Seminoma cells, unlike most lymphoma cells, have distinct cell membranes, abundant glycogen-rich cytoplasm, and rounded but focally flattened central nuclei with one or a few prominent nucleoli (Figure 3). Lymphomas tend to have smaller cells with less cytoplasm and a higher nuclear to cytoplasmic ratio. They show diffuse intertubular infiltration with recognizable tubular remnants. This characteristic intertubular pattern of growth of lymphoma is initially suggestive of the diagnosis in many cases but is not specific. The cells of spermatocytic seminoma are glycogen free, polymorphous, and of 3 distinct types.15 Embryonal carcinoma has a characteristic epithelioid appearance that frequently forms glandular, papillary, or tubular structures. Furthermore, in contrast to both seminoma and embryonal carcinoma, lymphomas lack precursor intratubular germ cell neoplasia, unclassified type. Although lymphoma cells may invade into the seminiferous tubules, they do not show the regular basal alignment within the tubules as in intratubular germ cell neoplasia, unclassified type. Testicular lymphomas are often positive for CD45 and CD20, but they are negative for OCT3/4 and placental alkaline phosphatase.34 

Viral and granulomatous orchitis have heterogeneous and benign-appearing inflammatory cellular infiltrates, in contrast with the more homogeneous and malignant-appearing infiltrate of lymphoma (Figure 4, A and B). In addition, viral orchitis has a patchy rather than a diffuse distribution.15 

The most common type of primary testicular lymphoma is diffuse large B-cell type. It usually presents as a painless unilateral testicular mass in older men. Constitutional symptoms such as fever, weight loss, anorexia, and night sweats are often present. Treatment is complex and dependent on the initial characteristics of the patient. An orchiectomy, especially in early-stage disease, is advantageous because it provides tissue for pathologic evaluation and removes a sanctuary site, as the blood-testis barrier makes testicular tumors inaccessible to systemic chemotherapy. There is a high risk of extranodal relapse even in cases with localized disease at diagnosis; therefore, an adjunctive chemotherapy or radiotherapy regimen is necessary. It is important to identify primary testicular DLBCL correctly and distinguish it from other entities because of differences in therapy, management, and prognosis.