Immunohistochemically, malignant MALT lymphoma cells express markers of B-cell lineage, but are distinct from follicular lymphomas (which express CD10), mantle cell lymphomas (which express cyclin D1 and CD5), and small lymphocytic lymphomas (which express CD5 and CD23) .
Typically, the neoplastic MALT lymphoma cells coexpress CD20+ and surface light-chain restriction but are negative for CD10 and CD5. Some researchers have documented expression of CD5 in MALT lymphomas, which is rare. Aberrant CD5-expression is thought to be a marker of early dissemination and aggressive behavior in some patients, but CD5 expression in localized, indolent MALT-type lymphomas has been reported .
CD5 is a T-cell antigen that is expressed on normal B-cells, in cord blood, adult peripheral blood, spleen, and lymph nodes. CD5 is also occasionally expressed on B-cell neoplasms, but its clinicopathological significance in low-grade B-cell non-Hodgkin's lymphomas (NHL), notably MALT lymphomas, remains obscure . In the oral cavity, previous report described that primary MALT lymphoma with the expression of CD5 occurred in the tongue . Although MALT lymphoma expressed CD5, this MALT lymphoma did not recur. However, we experienced that CD5 positive expression of MALT lymphoma in buccal mucosa occurred recurrence. Whether CD5 expression is relevant to the prognosis of patients with MALT lymphoma is controversial .
Kojima and colleagues reported that MALT lymphoma occurred in the soft palate and recurred [6, 15]. This MALT lymphoma showed positivity for kappa but negativity for CD5.
Compared with our primary case and Kojima and colleagues' case, our primary case expressed CD5, kappa-, and lambda-light chain. The presence of both kappa- and lambda-light chain-restricted B-cell populations in B-cell lymphomas, including MALT lymphoma, is an unusual findings .
Edinger et al. reported 2 other examples of primary cutaneous marginal zone lymphomas that express both kappa- and lambda-light chain-restricted B-cell populations .
In this study, kappa- and lambda-light chains were clonally related to each other . Fujiwara et al. described the aggressive B cell lymphoma with kappa- and lambda- dual light chain expression . They considered that kappa- and lambda- dual light chain expression was involved in the aggressiveness of B cell lymphoma.
Harby et al. observed that the frequent lambda- light chain gene rearranged and expressed in murine CD5+ B lymphoma cells and these lymphoma cells had a functional kappa- chain allele when induced for kappa- chain expression with bacterial lipopolysaccharide . This mechanism in CD5+ B lymphoma cells may be related to the recurrence of our case.
Gastric MALT lymphomas are correlated with Helicobacter pylori gastritis because colonization of Helicobacter pylori in the gastric mucosa results in lymphoid infiltration and the formation of acquired lymphoid tissue .
Moreover, T cells are specific for Helicobacter pylori and neoplastic B cells in gastric MALT lymphomas generate autoantibodies .
We considered that the pathogenesis of oral MALT lymphoma is related to Helicobacter pylori infection; however, Helicobacter pylori were not detected by immunohistochemical analysis or endoscopy in either the primary or the recurrent tumors. These results suggest that oral MALT lymphoma etiology is a result of several distinct factors and not exclusively Helicobacter pylori infection.
Although it is well known that MALT lymphomas frequently occur in the background of inflammatory disorders when B cell clones become independent in their growth , the development of oral MALT lymphoma is largely unknown. Present studies are considering allergies to metals and periodontitis as factors for the development of MALT lymphoma of the oral cavity. Therefore, further investigations are necessary to clarify the mechanism of the development of oral MALT lymphoma.
Our study suggests that immunohistochemical expression of CD5, kappa, and lambda in oral MALT lymphoma have the risk of recurrence. Our study raises the possibility to decide the therapeutic strategy whether oral MALT lymphoma expresses CD5, kappa, and lambda.
Although the present patient had no recurrence over 6 months after excision of the recurrent tumor, careful observation is needed, because the clinicopathological significance of MALT lymphomas with this rare phenotype remains obscure .
We first described the recurrence of CD5 positive MALT lymphoma in the oral cavity and compared the immunohistochemical expressions of CD5, lambda, and kappa between the primary and recurrent tumors.