Breast cancer cells might interact through CXCR5/CXCL13 interactions to organise cellular cluster formation and compartmentalisation as has been shown for B cells in renal allografts (Steinmetz et al, 2005) and in salivary glands of patients with Sjogren's syndrome (Barone et al, 2005). The gene discussed is CXCL13; the disease is Sjogren syndrome.