A 52-year-old female with relapsed lambda light chain myeloma, FISH 1q gain, developed bilateral pleural effusion. Her pleural fluid cytospin sample showed many large atypical plasma cells (May-Grünwald-Giemsa stain, x100 objective). She was treated with Taquetamab to partial response, resolution of pleural effusion, and normalisation of serum-free light chain.