Tumours with sizes smaller than 100 mm3, formed from SP cells of both MCF-7/HER2-18 (Figure 3B) and GCC-BC4 (Supplementary Figure S2) lines, were negative for ERα and positive for nuclear IGFBP7, consistent with the localisation of these markers in SP, as shown in Figure 3A. The gene discussed is IGFBP7; the disease is neoplasm.