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Unusual cohesive growth pattern of diffuse large B‐cell lymphoma mimicking metastatic carcinoma

A 59-year-old male presented with an enlarging right axillary mass of 6 months duration. A computed tomography scan revealed a large right axillary lymph node measuring 6 6 cm and a Bosniak 4 cystic mass in the right kidney measuring 4 0 cm. Fine needle aspiration cytology of the right axillary lymph node showed cohesive clusters of large tumour cells with pleomorphic nuclei (top left). A provisional diagnosis of metastatic carcinoma was rendered. The patient subsequently underwent ultrasound guided core biopsy of the lymph node. Histology showed infiltrative nests of tumour cells exhibiting vesicular nuclei and single to multiple nucleoli, with intervening blood vessels (top right). Immunohistochemical studies showed the tumour cells to be positive for CD45, CD20 (bottom left), CD79a (bottom right), CD30, BCL6, BCL2, MUM1 and MYC. The tumour cells were negative for AE1/3, CK7, P40, TTF1, E-cadherin, S-100, CD3, CD10, Cyclin D1 and ALK1. Only rare tumour cells were positive for PAX8. A final diagnosis of diffuse large B-cell lymphoma (DLBCL) was rendered. Lymphomas, such as anaplastic large cell lymphoma (ALCL), commonly display sinusoidal cohesive growth patterns, mimicking metastatic carcinoma. However, DLBCLs with highly cohesive growth patterns are unusual and rarely reported in the literature. The patient underwent 6 cycles of cyclophosphamide, doxorubicin, vincristine, prednisone with rituximab chemotherapy and showed clinical response.