A new study proposes that the cancerous behavior of B cells in a subtype of diffuse large B-cell lymphoma is caused by excessive activity of the linear ubiquitin chain assembly complex (LUBAC) complex, which underlies abnormal NF-κB signaling. Two rare germline single-nucleotide polymorphisms in the RNF31 gene have been identified as being responsible. The use of a small inhibiting peptide may downregulate the abnormal LUBAC activity and counteract neoplastic cell growth.