EditorSister Mary Joseph's nodule is an umbilical metastatic nodule from an intra-abdominal tumour.1 The primary origin is usually the gastrointestinal or genital system, but on rare occasions, this pathology originates from lymphoma. [2][3][4] We describe herein a case of diffuse large B-cell lymphoma (DLBCL) infiltrating only in the umbilicus, histologically presenting as epidermotropism, as an atypical histological presentation of B-cell lymphoma.A 36-year-old Japanese man consulted with us about a 1-week history of a painful nodule on the umbilicus. He had been treated for DLBCL developing in the pancreas with a regimen of R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisolone). On the first visit, physical examination disclosed an infiltrated, reddish nodule on the umbilicus (Fig. 1a). Computed tomography (CT) of the abdomen revealed significant enlargement of a tumour at the umbilicus (Fig. 1b). A biopsy specimen from the navel revealed atypical large cells densely infiltrating through the dermal papillae to the subcutaneous tissue, and epidermotropism with involvement of the overlying epidermis (Fig. 2a). Immunohistochemical staining revealed that these large cells were positive for CD10 (Fig. 2b), CD20 (Fig. 2c), CD45, CD79a (Fig. 2d), bcl2 and c-myc and negative for CD3, CD5, CD56, bcl6, and multiple myeloma oncogene-1. From the above data, we diagnosed DLBCL on the umbilicus, presenting as Sister Mary Joseph's nodule.Because the histological finding of epidermotropism in B-cell lymphoma is extremely rare, we employed immunohistochemical staining for matrix metalloproteinase (MMP)-2, MMP-9, and E-cadherin to investigate the underlying mechanisms. Immunohistochemical staining revealed a lack of E-cadherin in tumour-infiltrated areas of epidermis (Fig. S1a, Supporting Information). Moreover, lymphoma cells were positive for MMP-9 (Fig. S1c, Supporting Information) and negative for MMP-2 (Fig. S1b, Supporting Information).In this report, we have described a case of DLBCL infiltrating only the umbilicus, presenting as a Sister Mary Joseph's nodule and showing epidermotropism histologically. To inves-