Primary Testicular Mantle Cell Lymphoma in a 23-Year-Old Man: A Case Report and Review of the Literature

Background: Primary testicular mantle cell lymphoma (PTMCL) is a very rare disease, mostly occurred in elderly men, usually diagnosed at an advanced stage. Mantle cell lymphoma (MCL) has a distinctive immunophenotype, positive for CD5 and cyclin D1, but negative for CD10 and CD23. The genetic hallmark of MCL is t(11;14)(q13;q32). Case presentation: Here we reported a case of 23-year-old man who presented with a tumor in the testis. Surgical excision and pathological examination revealed the lesion was a primary testicular mantle cell lymphoma with aberrant expression of CD10 and loss of CD5. Conclusion: This study reports the rst case of PTMCL in a 23-year-old man with aberrant expression of CD10 and loss of CD5, summarizes PTMCL reported in PUBMED and found that CD5 might be an independent factor that inuences not only the diagnosis but also the prognosis of MCL.


Background
Primary testicular non-Hodgkin's lymphoma (PTL) is a rare disease, which represents 1-2% of all non-Hodgkin's lymphoma and about 9% of testicular neoplasms. It is the most common testicular malignancy in men over 60 years of age. Most of PTLs (80-98%) are diffuse large B cell lymphoma (DLBCL) and rare subtypes include mantle cell lymphoma, NK/T-cell lymphoma, follicular lymphomas, peripheral T-cell lymphoma, extranodal marginal zone lymphoma and ALK − large cell lymphoma [1][2][3][4][5]. Primary testicular mantle cell lymphoma (PTMCL) is very rare, only reported in sporadic case reports. Mantle cell lymphoma (MCL) is characterized by t(11;14)(q13;q32) rearrangement, which juxtaposes CCND1 on chromosome 11q13 with IGH on chromosome 14q32. Morphologically, MCL is divided into classical and variant subtype, the latter consists of aggressive variants (blastoid and pleomorphic) and other variants (smallcell and marginal zone-like). MCL has a typical immunophenotype, positive for pan B-cell markers, CD5 and cyclinD1, but negative for CD10 and CD23 [6]. However, few cases of MCL that express CD10 and lack of CD5 expression have been reported [7][8][9], which makes diagnosis more challenging. Here we reported a 23-year-old PTMCL with aberrant immunophenotype, reviewed the clinicopathological charateristics of PTMCL reported in PUBMED and investigated the clinical signi cance of unusual immunophenotype.

Case Presentation
A 23-year-old man accidentally found his left testicular enlargement in April 2018, without pain or any other symptoms and had a testicular biopsy. Post-biopsy pathological diagnosis considered B cell lymphoma. Immunohistochemical (IHC) staining showed CD20, BCL2, CD10 and MUM1 were positive CD3, CD5, BCL6, C-MYC, CyclinD1, SOX11 and CD30 were negative, supporting diffuse large B cell lymphoma, germinal center B cell subtype (DLBCL, GCB; HANS classi cation).
Soon he underwent a left orchiectomy, the neoplastic mass was measured 5.5cmΧ4.5cmΧ4cm with a soft, white to tan cut surface. Histologically, the mass was occupied by diffuse in ltrative medium to large-sized atypical lymphoid cells, which resembled bastoid cells with scant cytoplasm, irregular nuclear contours, dispersed chromatin, high N:C ratio, and a high mitotic rate. Residual seminiferous tubules were entrapped in lymphomatous tissue. In some areas a so-called 'starry sky' pattern was present. The paramount consideration for the differential diagnosis in a 23-year-old man include 1 lymphoblastic lymphoma (LBL); 2 Burkitt's lymphoma(BL) 3 DLBCL or high-grade B-cell lymphoma(HGBL). Based on the pre-operation pathological result and morphology, IHC staining with a panel of markers (CD20, CD3, CD5, CD10, MUM1, BCL2, BCL6, C-MYC, Ki67, TdT, CyclinD1) were performed. The result showed CD20, CD10 and BCL2 were positive, CD3, CD5, BCL6, C-MYC, MUM1 and TdT were negative, and Ki67 proliferation rate was up to 90% ( Figure 1). CD20 expression and high Ki67 proliferation rate con rmed it an aggressive B-cell lymphoma. BL was excluded due to negative C-MYC and positive BCL2. Positive CD20 and negative TdT helped exclude the diagnosis of LBL. Unexpectedly, CyclinD1 was diffusely and strongly positive compared to the former biopsy sample, which really made us confused. Previous studies showed CyclinD1 + DLBCL was often considered to be a post-germinal center-type lymphoma without CCND1 gene alteration, and negative for SOX11 [10,11]. As to our case, can it be a DLBCL (GCB) with aberrant expression of CyclinD1? Or is it possible a MCL? Although cases of CD5 -MCL have also been reported, until now such a young patient with MCL is still rather rare. That's why MCL was not considered as one of the differential diagnosis initially. While SOX11 is positive in >90% of MCL including CyclinD1and blastoid cases [6], we performed IHC staining with SOX11, and found SOX11 was positive ( Figure 1). Despite negative CD5, both positive CyclinD1 and SOX11 indicated it was most likely MCL. To further clarify the diagnosis, IGH/CCND1 rearrangement was detected by uorescence in situ hybridization (FISH) analysis, and 72.5% of the examined cells were positive ( Figure 1). Therefore, the diagnosis of MCL was con rmed.
The general conditions of the patient were evaluated by positron emission tomography-CT (PET-CT) before and after surgery, which both revealed no super cial lymphadenopathy, no abnormal uptake within right testis and no evidence of metastatic disease. Biochemical assays for carcino-embryonic antigen, alpha-fetoprotein and beta-human chorionic gonadotrophin were within normal range. In addition, a bone marrow biopsy demonstrated normal cellularity with tri-lineage hematopoiesis and no evidence of lymphoma. These indicated that MCL was limited to the left testis, a de nite diagnosis of PTMCL was thus made.

Discussion And Literature Review
The most unique of our case is the site and age, which make us easily ignore MCL. We investigated 58 cases of PTL diagnosed between January 2013 to December 2019 at Tianjin Medical University Cancer Institute & Hospital, there was only one case of PTMCL. Contemporaneously, there were 5761 cases of non-Hodgkin lymphoma (NHL) and 179 cases of MCL. The proportion of PTL is 1% (58/5761) of all NHL, which is consistent with that reported in previous studies. PTMCL is only 0.17‰ (1/5761)of all NHL, 0.6‰ of all MCL (1/179) and 1.7% of PTL (1/58) in our database. Moreover, we searched PTMCL reported in PUBMED between the year 1996 and 2020, only found seven cases, and summarized in Table  1 and 2. Table 1 show that PTMCLs occur in middle-aged to older men, ranging from 45 to 87.5 years old, the average age is 69.8 years. Most PTMCLs are unilateral, prefer to involve right testis and present with advanced stage, usually stage . Previous statistics show the spectrum of NHL subtype varies with age, the relative frequency of MCL is zero before 30 years of age [12]. These indicate our case is the youngest patient with PTMCL that have ever been reported.
Thus, a 23-year-old man with testis lymphoma, with simultaneously existed aberrant immunophenotype of CD5 and CD10 make the diagnosis rather challenging. However, the morphology demonstrates the tumor consists of blastoid cells, reminding us of the differential diagnosis of the HGBL described in the 2017 revised WHO classi cation [6]. The most important differential diagnosis consist of LBL, BL, CyclinD1 + DLBCL, and HGBL. IHC and molecular genetic analysis are helpful. The expression of TdT assists in the diagnosis of LBL. BL is characterized by an MYC translocation with strong expression of C-MYC, and negative BCL2. CyclinD1 + DLBCL do not harbor CCND1 translocation and lack SOX11 expression. The presence of CCND1 translocation can also exclude HGBL. However, what's really puzzling is the inconsistent IHC staining of CyclinD1 and SOX11 in biopsy and orchiectomy sections. To explore the factors that result in the staining difference, we reviewed the biopsy sections and found that the biopsy sections were frozen before making para n sections. Frozen tissue often makes morphological features and IHC staining suboptimal, leading to misdiagnosis. As to our case, considering the patient's age, immunophenotype with negative CD5, CyclinD1 and SOX11 as well as positive CD10 excluded the diagnosis of MCL resulting in misdiagnosis of the biopsy specimen. Therefore, every step in the process of making para n sections is vital to morphology, immunophenotype and molecular genetics of histological specimen, which are all indispensable to the correct diagnosis.
In addition, the clinicopathological features of CD5and CD10 + MCL have also been reported, but cohort study are less and controversial. Some supposed the clinicopathological features of CD5 -MCL was similar to that of CD5 + MCL [19]. Some reported that all CD5 -MCL cases showed classical morphology with a low Ki67 proliferation rate (<5%), and appeared to have a better prognosis and overall survival than classic MCL [20]. However, only 12 cases with follow-up data were involved in these previous studies.
Recently, 58 cases of CD5 -MCL were involved in a relatively comprehensive study, and no signi cant difference was found between the morphology of CD5and CD5 + MCL, while patients with CD5 -MCL showed a signi cantly longer progression-free survival and a tendency for longer overall survival than CD5 + MCL patients. Furthermore, high Ki67 proliferation rate and clinical stage were not associated with prognosis in CD5 -MCL. CD5 was thought to be an independent prognostic factor in patients with MCL [8].
CD10 is usually expressed by centrocytes and centroblasts in the germinal center (GC) and by their neoplastic counterparts, rare cases of MCL have been reported to express CD10. However, it is still controversial whether CD10 expression in MCL is related to GC. Some estimated CD10 expression in MCL did not re ect derivation from GC B cells [14]. Others suggested CD10 expression was related to a distinct GC signature in MCL [26]. Moreover, CD10 + MCL showed a female predominance, more often had a diffuse growth pattern, and was more frequently associated with variant morphology. But there was no signi cant difference in the prognosis between CD10 + and CD10 -MCL [7,14,21,26]. In conclusion, CD5 might be an independent prognostic factor of MCL and CD10 + MCL might have some special pathological features.
Our patient underwent localized radiotherapy and six cycles of R-DHAP chemotherapy. Currently, he continues to be healthy with no apparent manifestation of the disease by PET-CT. These indicate that PTMCL con ned to the testis with loss of CD5 seems to have a better prognosis. However, cases of CD5and CD10 + MCL involved in previous studies are limited, further study is still needed for exploring the biological and clinicopathological signi cance of these rare cases.
To our knowledge, this is the youngest PTMCL so far, and aberrant CD5 and CD10 expression aggravates its rarity. Whether CD5and CD10 + MCL is a new entity still needs a larger cohort with close follow-up, which might provide certain basis for strati ed treatment of MCL in the future.

Conclusions
In summary, we have reported the rst case of PTMCL in a 23-year-old man with aberrant expression of CD10 and loss of CD5. Integration of morphology, immunophenotype and molecular genetics should be taken into account in order to make precise diagnosis of a young man with MCL.