Primary cutaneous marginal zone lymphoma with subclinical cutaneous involvement and biclonality.

Primary cutaneous extranodal marginal zone lymphoma (MZL) of mucosa-associated lymphoid tissue (MALT) represents a monoclonal B-cell neoplasm that typically presents with papules, plaques or nodules. We describe a patient with a primary cutaneous MALT lymphoma with unusual clinical features and an unusual immunophenotype. Conventional microscopy together with immunohistochemistry and in-situ hybridization showed the presence of lymphoma in normal-appearing and minimally erythematous skin as well as in clinically involved skin. Furthermore, at least two distinct clones were shown, one of which had κ-light chain restriction, and the other of which had λ-light chain restriction. This case represents a newly described clinical appearance of primary cutaneous MZL and shows that some patients may have more than one neoplastic clone.